Biomedical subjects

J E McElhaney

Publications and source records attributed to J E McElhaney.

At least 19 recordsLinked to original sources

PubMed2001

Granzyme B: a marker of risk for influenza in institutionalized older adults.

Risk for influenza increases with age while cellular immune responses decline. This was a prospective study to determine the relationship between cytokine and granzyme B levels in peripheral blood mononuclear cells stimulated with live influenza virus, and subsequent influenza illness. Granzyme B levels were lower in the group who later developed symptomatic laboratory-confirmed influenza (n=10) compared to the group who did not (n=90) (ANOVA, P=0.024). In contrast, none of the cytokine levels were related to the development of influenza. Thus, granzyme B is a potential marker of influenza risk in older adults.

Aged↗

PubMed2000

Standing orders for influenza vaccination increased vaccination rates in inpatient settings compared with community rates.

BACKGROUND: Hospitalization of older adults during the period of influenza vaccination in the fall of each year presents a barrier to immunization against influenza. This study evaluates a program using standing orders for influenza vaccination to increase vaccination rates among hospitalized older adults and to determine the effect of vaccination on readmission rates for influenza-like illness. METHODS: An influenza vaccination program using a standing order policy was implemented to vaccinate all consenting persons 65 years and older prior to hospital discharge. This was a prospective, single center, cohort study in a tertiary care university teaching hospital during an 8-week vaccination period in the fall of 1994 and follow-up during the subsequent influenza season. The vaccination status of each patient was recorded as no vaccination, vaccination received in hospital, or vaccination in the community prior to or after the hospitalization. Hospital vaccination rates were compared with the rate of vaccination of older adults in the community. During the subsequent influenza season, the number of subjects reporting symptoms of influenza-like illness (ILI) or who were readmitted to hospital with influenza-related illness was compared in an analysis of vaccinated versus unvaccinated subjects. RESULTS: Seven hundred and sixty-one patients were interviewed, and 332 of these individuals had been vaccinated in the community prior to their hospital admission. Of the remaining 429 unvaccinated patients who were eligible for vaccination in the study, 171 were vaccinated in our immunization program, eight were vaccinated in the community after discharge, and 244 were not vaccinated. We were able to increase the absolute vaccination rate by 22%, when compared with community rates, with our immunization program. The number of subjects with ILI symptoms or readmission to hospital was too small to compare the vaccinated to the unvaccinated group in the study. CONCLUSIONS: An inpatient influenza immunization program using a standing order policy was able to target a particularly high-risk subset of persons 65 years and over who might otherwise have not received influenza vaccination.

Aged↗

PubMed2000

Mortality and institutionalization following hip fracture.

OBJECTIVES: To identify determinants of mortality and institutionalization after hip fracture and to identify those older hip fracture patients at high risk of death or institutionalization after hip fracture. DESIGN: Population-based prospective inception cohort study of hip fracture patients; patients were assessed in the hospital and at 3 months following the hip fracture. SETTING: Edmonton area hip fracture patients admitted to one of two Edmonton, Alberta, Canada, acute care centers between July 10, 1996, and August 31, 1997. PARTICIPANTS: Patients were residents of the Edmonton area and over the age of 64. Those who had previously fractured the same hip within the past 5 years or had some pathological condition underlying the hip fracture were excluded. Of 610 eligible patients, 558 contributed some baseline information and were included in the mortality analysis; the institutionalization analysis was restricted to the 338 patients who lived in the community before fracture, survived the 3-month period postfracture, and had completed a 3-month follow-up interview. MEASUREMENTS: The baseline interview was done in the hospital to assess mental status, prefracture physical function, prefracture health perception, and prefracture social support. The 3-month follow-up interview was done by phone to assess physical function, health perception, and social support 3 months postfracture. Demographic and comorbidity information was collected from medical records. RESULTS: Low mental status in hospital was found to increase the chances of mortality and institutionalization, and male gender was found to increase mortality risk fourfold. Each additional 10 years of age increased the risk of institutionalization approximately 2.5 times. Patients with lower postfracture physical function had at least five times the risk of institutionalization compared to patients with high postfracture physical function. CONCLUSIONS: Cognitive impairment, older age, and gender were associated with increased risk of poor outcome following hip fracture. The socioeconomic variables--social support and health perception--did not contribute significant additional information in explaining mortality or institutionalization risk. While demographic factors cannot be modified, physical function 3 months postfracture may be amenable to intervention and may reduce the risk of institutionalization. Intervening to increase postfracture physical function may be particularly beneficial to older patients, or to those who are cognitively impaired.

Aged↗

PubMed1999

Validity of the confusion assessment method in detecting postoperative delirium in the elderly.

In this prospective cohort of 71 elderly patients undergoing cardiac surgery, each subject was interviewed before and after surgery to detect incident delirium using the Confusion Assessment Method (CAM), the Mini-Mental State Examination (MMSE), the Clock Test, and a health record review. The first 41 were assessed by a physician and the remaining 30 by two study nurses. Delirium was then diagnosed by a physician using DSM-III-R criteria. Delirium was present in 23 subjects (32.4%). The sensitivity of the CAM differed significantly when administered by physicians compared to nurses (1.00 vs. .13). When standard cutoffs were used, neither the MMSE nor the Clock Test were found to be sensitive markers for delirium (.30 and .09, respectively). Recognition of delirium by charting was superior in nurses compared to physicians (.83 vs. .30). We conclude that the sensitivity of markers for delirium, such as the CAM and health record documentation, is dependent on the training background of the operator.

Aged↗

PubMed1999

Incidence and risk factors for delirium and other adverse outcomes in older adults after coronary artery bypass graft surgery.

OBJECTIVE: To determine the incidence and risk factors for delirium after coronary artery bypass graft (CABG) surgery. DESIGN: Prospective cohort. SETTING: Cardiac surgery units of a tertiary care hospital. PARTICIPANTS: Consecutive patients over age 65 years undergoing elective CABG surgery. Exclusion criteria included preoperative sensory or language barriers. INTERVENTIONS: Each patient was assessed within 24 h before surgery for baseline demographic, medical and functional data. Incident delirium (within four postoperative days) was diagnosed by a study physician. Nine potential risk factors for delirium were subjected to univariate and multivariate analysis. MAIN RESULTS: Of 75 consenting patients, three died during or soon after surgery and one was still comatose at follow-up. Of the remaining 71 participants, 23 (32%) experienced delirium. Those with delirium were more likely than those without delirium to have a history of a stroke (21% versus 4%, respectively, P=0.032) and to have had a longer duration of cardiopulmonary bypass (CPB) (113 mins versus 95 mins, respectively, P=0.025). A tendency to have experienced low cardiac output (83% versus 58%, respectively, P=0.061) postoperatively was also noted. Multivariate analysis confirmed past stroke and duration of cardiopulmonary bypass as risk factors. CONCLUSIONS: Delirium in the elderly after CABG surgery is common. Its occurrence may be predisposed by a history of a stroke and precipitated by a longer duration of CPB.

Age Factors↗

PubMed1998

Immune response to influenza vaccination in institutionalized elderly: effect on different T-cell subsets.

Humoral and cellular immunological responses to influenza vaccination were measured in volunteers in a long-term care facility. All participants were vaccinated with the commercially available 1994-95 trivalent influenza vaccine and blood samples were collected before and 6 and 12 weeks after vaccination. Cytokine and granzyme B in peripheral blood mononuclear cell (PBMC) cultures after virus stimulation, and serum antibody titres were measured for each of these time points. In general, the measures of the immunological response to vaccination were low and variably significant. The major finding was the difference with respect to post-vaccination measures for the two strains of influenza A contained in the vaccine. Geometric mean antibody titres were significantly higher for A/Texas/36/91 at all time points in the study when compared to A/Shangdong/09/93. There was a corresponding rise for interleukin-10 (IL-10) to the A/Texas/36/91 strain while no increase in IL-10 was observed in A/Shangdong/09/93-stimulated cultures after vaccination. In contrast, granzyme B rose after vaccination only in cultures stimulated with A/Shangdong/09/93. Interferon-gamma levels were also significantly higher in these PBMC cultures. There was a poor interleukin-2 (IL-2) response to both strains of influenza A. These data suggest that different strains or subtypes of influenza A may preferentially enhance T-helper type 1 versus type 2 responses through vaccination in institutionalized seniors.

Adult↗

PubMed1998

Responses to influenza vaccination in different T-cell subsets: a comparison of healthy young and older adults.

T-lymphocyte responses to influenza vaccination were measured in healthy young and older adult volunteers. All participants were vaccinated with the 1995-96 trivalent influenza vaccine. Cytokine and granzyme B levels were measured in peripheral blood mononuclear cells (PBMC) cultures after virus stimulation, prior to and 4 and 12 weeks after vaccination. The major findings in the older adult group were the different types of helper T-cell (Th) responses to each of the vaccine strains of virus and a very poor cytotoxic T lymphocyte (as measured by granzyme B) response to vaccination. IL-10, which is produced in a Th-type 2 response, was higher in PBMC stimulated with A/Texas/36/91 (H1N1) compared with A/Johannesburg/33/94 (H3N2); this difference was more marked in the PBMC from older compared with younger adults. In contrast, IL-2, which is produced in a Th-type 1 response, was measured in the same cultures and was significantly higher in A/Johannesburg/33/94-stimulated PBMC. IFN- gamma levels were highest in the PBMC stimulated with B/Harbin/7/94. The greatest age-related difference was the level of granzyme B in all virus-stimulated PBMC from the young compared with the older adult group. The strain of influenza virus contained in the vaccine, as well as the age of the subject, appear to be very important determinants of the T-cell response to vaccination.

Adult↗

PubMed1998

Assessment of markers of the cell-mediated immune response after influenza virus infection in frail older adults.

The purpose of this study was to determine whether measures of the cell-mediated immune response to influenza virus could be used as markers of influenza virus infection. We studied 23 subjects who developed upper respiratory, lower respiratory, or systemic symptoms during a small outbreak of influenza in a nursing home population. Influenza virus culture from nasopharyngeal swabs yielded influenza virus isolates from 7 of the 23 subjects. Only three of the subjects had a fourfold rise in antibody titer to the influenza virus antigen positivity after the infection. Granzyme B and cytokine levels were measured in peripheral blood mononuclear cells (PBMC) obtained from all subjects and stimulated with live influenza virus. Elevated granzyme B levels in virus-stimulated PBMC in combination with lower respiratory tract or systemic symptoms in study subjects was a significant predictor of culture-confirmed influenza virus infection compared to those from whom influenza virus could not be identified. Cytokine levels did not distinguish between the two groups in a similar type of analysis. Granzyme B in combination with the clinical profile of symptoms may be a useful retrospective marker for influenza virus infection.

Aged↗

PubMed1997

Humoral and cellular immune responses following vaccination with purified recombinant hemagglutinin from influenza A (H3N2) virus.

Adults were immunized with either baculovirus-expressed, purified recombinant hemagglutinin (rHA) from influenza A/Beijing/32/92 (H3N2) virus or saline placebo and evaluated for humoral and in vitro cellular immune responses. Compared with responses in placebo recipients, vaccinees had greater postvaccination H3(Beijing/32) HA (H3)-specific lymphoproliferation and interleukin (IL)-2, IL-10, and interferon-gamma (IFN-gamma) production. Mean increases in the production of IL-10 (> or = 20-fold) and IL-2 (10-fold) were relatively greater than that of IFN-gamma (4-fold) or IL-4 (no change). Serum H3 antibodies were induced in 80% of rHA recipients, and the rise in antibody titer was significantly correlated with changes in IL-2, IL-10, and IFN-gamma concentrations. Vaccination with rHA only minimally enhanced anti-influenza virus cytotoxic T lymphocyte activity. These data demonstrate that rHA immunization of adults elicits a significant recall response by memory B and T lymphocytes and suggest that the cytokine response to vaccination has a T helper cell type 0-like profile.

Adolescent↗

PubMed1996

The cell-mediated cytotoxic response to influenza vaccination using an assay for granzyme B activity.

The measurement of cytotoxic T lymphocyte (CTL) activity through 51Cr assays is a very labour intensive method for studying cytotoxicity in human CTL due to the necessary preparation of autologous targets for the assay. An assay for granzyme B, one of a family of serine proteinases implicated in the 'lethal hit' that leads to target cell lysis, is an alternative simple measure of CTL activation. We measured granzyme B activity using its both preferred and unique substrate tert-butyloxycarbonyl-Ala-Ala-Asp-thiobenzyl ester (BAADT) in peripheral blood mononuclear cells (PBMC) obtained from influenza vaccinated subjects, and stimulated with live virus. We found that granzyme B activity increases in parallel and correlates with cytolytic activity as measured by 51Cr release assays in these virus-stimulated PBMC cultures. The assay was then used to measure the cell-mediated cytotoxic response to influenza vaccination in ten healthy elderly subjects. Peak granzyme B activity (day 6) was measured in lysates of PBMC stimulated with influenza virus, obtained from study participants before and after vaccination. We found a significant increase in granzyme B activity from pre-vaccination levels to 4 weeks post vaccination (pre=2.77 U/mg protein, post=7.23 U/mg protein, p=0.002) and a subsequent decline in the activity measured at 12 weeks post vaccination (4.34 U/mg protein, p=0.0007). Due to its substrate specificity which is unique within the family of serine proteases, this assay is highly specific for granzyme B. The assay also avoids the potential hazard of radioactivity (51Cr) in the clinical laboratory and the need for a gamma counter. The assay of granzyme B activity, therefore, provides a simple, specific and responsive method for measuring changes in cell-mediated cytotoxic activity resulting from influenza vaccination.

Adult↗

PubMed1996

Helper and cytotoxic T lymphocyte responses to influenza vaccination in healthy compared to diabetic elderly.

This study was designed to determine the effect of Type II diabetes mellitus in older adults on two measures of the cell-mediated immune response to influenza vaccination. Twenty-two elderly persons with diabetes mellitus were compared to 20 healthy seniors, all of whom were living independently in the community. Peripheral blood mononuclear cells (PBMC) were challenged in vitro with live influenza virus, pre-vaccination and 4 and 12 weeks post-vaccination. PBMC culture supernatants were assayed for IL-2 activity as a measure of the helper T-cell response to vaccination. The cytotoxic T-lymphocyte response was determined using an assay of granzyme B activity in PBMC lysates. Initial analysis of the data showed increased IL-2 production in post-vaccination PBMC cultures from the diabetic group compared to the healthy group. However, when vaccination histories were used in an analysis of variance, it was found that the difference between the two groups was related to vaccination history. Study subjects vaccinated one year prior to participation in this study compared to those who had not been previously vaccinated, demonstrated a significantly suppressed IL-2 response to vaccination. Type II diabetes mellitus had no effect on the IL-2 response to vaccination. The granzyme B response to vaccination was not significantly affected by previous vaccination and results were similar for the healthy and diabetic elderly groups.

Aged↗

PubMed1995

Multidrug transporter P-glycoprotein 170 as a differentiation antigen on normal human lymphocytes and thymocytes: modulation with differentiation stage and during aging.

P-glycoprotein 170 (P-gp), the multidrug transport pump, excludes drugs from the interior of cells and is inhibited by agents such as cyclosporin A (CsA), verapamil, and FK-506, which are also substrates for the P-gp pump. This work documents the age- and differentiation-related changes in P-gp on T and B lymphocytes from human blood or spleen, and its absence on most thymus and bone marrow cells. Analysis of rhodamine 123 (Rh123) dye efflux, and its inhibition by cyclosporin A, was used as a quantitative measure of functional P-gp, and reactivity with MRK-16 was used as a measure of P-gp surface expression. The dye efflux and phenotypic expression of P-gp+ PBMC appeared equivalent to that of a moderately drug-resistant cell line, although efflux is prolonged. The sensitivity to inhibition by CsA, cyclosporin G (CsG), and PSC833 of P-gp on PBMC, thymocytes, or T-cell lines varied with apparent cell-type specificity. Normal blood and splenic T- or B-cells included 50-80% of cells with surface P-gp (MRK-16+), which mediated CsA-sensitive dye export. The proportion of P-gp+ T- and B-cells was lowest among children under age 10 years, increased in adulthood, and decreased after age 60. Thymus included 30% of P-gp+ cells mediating CsA-sensitive dye export, including CD3-4-8- progenitors and mature CD3hi CD4+8- or CD4-8+ thymocytes. Mature T-cells in cord or adult blood, spleen, and bone marrow included a large proportion (50-60%) with efficient CsA-sensitive dye export, preferentially among the CD45RA+ subset. Monocytes from all tissue sources, and most bone marrow cells, expressed surface P-gp but retained Rh123, suggesting the absence of a functional dye export mechanism. In vitro mitogen-stimulated PBMC T and B lymphocytes lost P-gp function within 4-24 hr, consistent with the observation that P-gp was reduced on antigen-experienced CD45R0+ T-cells in vivo. Drug export by P-gp may protect lymphocytes from toxic effects of CsA, and may contribute to the immunosuppressive effects of such drugs. The developmentally regulated expression of P-gp function on lymphocytes, and its modulation on activated T- or B-cells, suggest an important role in normal immune development.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1995

Vaccine-related determinants of the interleukin-2 response to influenza vaccination in healthy young and elderly adults.

This study was designed as a parallel-groups comparison of trivalent preparations of split-virus vaccine (SVV) and whole-virus influenza vaccine (WVV) in healthy young and elderly adults. Interleukin-2 (IL-2) was measured in the supernatants of peripheral blood mononuclear cell (PBMC) cultures stimulated with live virus preparations of the two strains of influenza A contained in the vaccine. The duration of increased in vitro IL-2 production after vaccination was significantly different between the two strains of virus. A/Beijing/353/89 resulted in an IL-2 response that was quite short (< 7 weeks) while the response to A/Texas/16/89 was much more prolonged (> 12 weeks). In the first 12 weeks after vaccination, there was no difference in IL-2 levels between SVV and WVV recipients in either the young or elderly groups. The duration of the response to A/Texas/16/89 was slightly longer in WVV recipients as measured at 26 weeks postvaccination. The viral strain contained in the vaccine appears to be an important variable in determining the duration of the IL-2 response to vaccination.

Adult↗

PubMed1995

Changes in CD45 isoform expression vary according to the duration of T-cell memory after vaccination.

Healthy young (< 40 years) and elderly (< 60 years) adults were immunized with the 1992-1993 preparation of trivalent influenza vaccine, and changes in CD45 isoform expression on peripheral blood lymphocytes were measured in the pre- and postvaccination periods. Fluorescence-activated cell sorter analysis was used to study T-cell subsets in fresh peripheral blood lymphocytes (day 0) and after 6 days of culture with live influenza virus. We have reported previously that the interleukin-2 response to the stimulating strain of virus, A/Texas/16/89, did not decline until 26 weeks postvaccination. In ex vivo CD4+ subsets, this interleukin-2 response was paralleled by a > 10% increase in the proportion of cells expressing the CD45RO+ phenotype following vaccination (p < 0.0001). In vitro stimulation had no effect on CD4+ subsets prior to vaccination but, after vaccination, was associated with a > 10% increase in CD45RA+RO+ cells (P < 0.0001). In addition, we have identified a change in the population of cells that express a CD45 isoform that is neither CD45RA nor CD45RO (CD45RA-RO-). At 26 weeks postvaccination, the proportion of CD45RA-RO- cells in ex vivo CD4+ peripheral blood mononuclear cells increased by approximately 15% from that measured at the earlier postvaccination time points (P < 0.0001). In vitro stimulation with influenza virus resulted in a further 20% increase in the proportion of CD45RA-RO- cells (P < 0.0001). The CD45RA-RO- phenotype may identify a population of cells undergoing apoptosis (programmed cell death) that limits the duration of helper T-cell (CD4+) memory after vaccination.

Adult↗

PubMed1994

Characterization of a granule-independent lytic mechanism used by CTL hybridomas.

The mechanism(s) by which CTL induce target cell lysis have not been clearly elucidated. Perforin and the cytotoxic cell proteinases (granzymes) contained within the granules of CTL and NK, have been implicated, but abundant evidence for the existence of alternate lytic pathways has accumulated. In this report we characterize the mechanism of killing used by two cytolytic hybridomas (PMM-1 and MD90) that express neither perforin nor the granzymes. These characteristics are compared with results obtained by using a representative Ag-dependent, granule-containing T cell clone in cytolysis assays. The major differences were that the granule-negative hybridomas could lyse a variety of target cells in the presence of cyclosporin and the absence of calcium. All the effectors could kill in the presence of protein synthesis inhibitors (cycloheximide and emetine) and induced DNA fragmentation in the target cells. The cytolytic hybridomas had to be stimulated to be cytolytic and this activation required the presence of calcium, was dependent on protein synthesis, and inhibited by the addition of cyclosporin. Although TNF was shown not be involved, the sensitivity of the target cells to lysis by the granule-negative killers correlated with the level of expression of Fas Ag. With the use of L1210 and an L1210 cell line transfected with Fas cDNA we demonstrated that these MD90 and PMM-1 kill the latter much more effectively and that this increase was effectively inhibited with anti-Fas Ab. Furthermore the lack of sensitivity to cyclosporin, cycloheximide, emetine, and EGTA was confirmed with these targets. We conclude that these two cytolytic hybridomas use the Fas lytic pathway to induce lysis in target cells.

Animals↗

PubMed1994

Split-virus influenza vaccines: do they provide adequate immunity in the elderly?

BACKGROUND: Senescence of T-cell function increases susceptibility to influenza with aging. In healthy elderly, we have found that inactivated whole-virus vaccine (WVV) effectively boosts helper T-cell (Th)-mediated immunity. Recently, however, the use of WVV has been superseded by split-virus vaccine (SVV) to questionably reduce adverse effects of vaccination. METHODS: Healthy young adults were compared to healthy elderly adults for their response to SVV. Peripheral blood mononuclear cells (PBMC) obtained pre-vaccination and 6 and 12 weeks post-vaccination, were cultured with live influenza virus, and supernatant IL2 activity was measured. RESULTS: Both groups showed an increase in in vitro IL2 activity by 6 weeks post-vaccination but IL2 decreased to pre-vaccination levels by 12 weeks. Young and elderly adults who had received WVV one year prior did not respond to SVV in this study. CONCLUSIONS: SVV does not provide Th-mediated immunity for the duration of the flu season and may actually suppress Th-mediated immunity in previous recipients of WVV.

Adult↗

PubMed1994

Prevalence of selected autoantibodies in different elderly subpopulations.

We have evaluated the prevalence of selected autoantibodies commonly utilized in rheumatologic practice in different elderly subpopulations grouped according to their clinical status. RF, ANA, double-stranded DNA antibodies, and antibodies to extractable nuclear antigens (ENA) were measured in the serum of all participants using standardized laboratory assays. One hundred and fifty-nine elderly subjects were enrolled, of whom 63 were classified as successfully aging elderly, 62 were ambulatory chronically ill residents of a nursing or Veterans home and 34 were patients attending an RA clinic. Prevalence of autoantibodies were compared to healthy adult blood donors. There was no statistically significant increase in autoantibodies in successfully aging elderly compared to healthy young controls. RF, ANA and ENA antibodies were significantly increased in only the chronically ill and RA sufferers. Antibodies to nDNA were absent in all groups. We conclude that autoantibodies commonly utilized in rheumatological practice are not globally non-specifically increased as a result of aging, but increase in prevalence in chronically ill elderly. Therefore assessment of health status is necessary to evaluate the clinical significance of these autoantibodies in the elderly.

Aged↗

PubMed1993

Changes in CD45 isoform expression after influenza vaccination.

In this study, we report the changes in the isoforms of CD45 expressed on T lymphocytes after influenza vaccination. Young adults were compared to an elderly group (26 participants/group) after vaccination with influenza split-virus vaccine. Peripheral blood mononuclear cells (PBMC) obtained pre-vaccination and 6 and 12 weeks post-vaccination were cultured with live influenza virus. Unstimulated and stimulated (5-day culture with virus) PBMC were labelled with fluorescent monoclonal antibody markers for CD3, CD4, CD8, CD45RA and CD45RO. When compared to the young controls, the elderly group had a higher proportion of CD45RO+RA- and, reciprocally, a lower proportion of CD45RA+RO- cells. In spite of these differences, both groups showed a progressive increase in the proportion of CD45RA+ T lymphocytes (CD4+ and CD8+) following influenza vaccination. In vitro stimulation with influenza virus resulted in a decrease in the proportion of CD45RA+RO- with a concomitant increase in the CD45RA-RO- population, both of which were observed only at 6 weeks post-vaccination. Although the phenotype of classical memory cells for recall antigen is CD45RO+, these results suggest that memory for influenza split-virus vaccine, exists in the CD45RO- population. More importantly, it should be noted that in spite of the decline in CD45RA+ cells with aging, the elderly group showed similar changes in the proportions of all cell phenotypes in response to vaccination, and to subsequent in vitro re-exposure to the virus.

Adult↗