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Biomedical subjects

S Baqar

Publications and source records attributed to S Baqar.

At least 19 recordsLinked to original sources
PubMed2001

Campylobacter jejuni enteritis.

We report the development of Campylobacter jejuni enteritis in a patient with preexisting humoral and cellular immune recognition of C. jejuni antigens. This is one of few studies in which the immunologic status of a person with regard to C. jejuni before and after C. jejuni infection is directly compared, and it is the only study of which we are aware that includes measurements of cellular immunity. The findings may be important to Campylobacter vaccine development efforts.

Antibodies, Bacterial↗
PubMed2001

Pre-exposure anti-Campylobacter jejuni immunoglobulin a levels associated with reduced risk of Campylobacter diarrhea in adults traveling to Thailand.

Diarrhea history questionnaires were administered to 369 U.S. military volunteers before and after deployment to Thailand. Additionally, blood samples obtained from a subset of 221 volunteers 1-3 weeks previously and 3-4 weeks after their deployment were tested by enzyme-linked immunosorbent assay for immunoglobulin A to Campylobacter jejuni. Stool samples from personnel (including volunteers) contracting diarrhea in Thailand were cultured for enteric pathogens. Overall, 35.2% (130 of 369) of questionnaire respondents reported one or more diarrhea episodes during their trip. Volunteers with pretravel anti-C. jejuni reciprocal titers < or = 450 were 1.6 times as likely to have had diarrhea during their stay in Thailand compared with those with pretravel titers > 450 (39.7% versus 25.3%; P = 0.05). The symptomatic seroconversion, or attributable Campylobacter diarrhea attack rate, for the 1-month exercise was 12.7% (28 of 221). The symptomatic seroconversion rate in nonimmune (titer < or = 450) volunteers was 17.1%, whereas that in immune volunteers was only 4.0% (P = 0.002). Campylobacter jejuni or C. coli were recovered from 32.9% (56 of 170) of stool samples cultured and were the most commonly identified enteropathogens. Campylobacter diarrhea was associated with elevated temperatures, fecal red cells, and fecal white blood cells. The results of this study show that Campylobacter continues to represent a significant health threat to Western travelers to Thailand, but many of these travelers have preexisting Campylobacter immunity that protects them from clinically significant Campylobacter enteritis.

Adult↗
PubMed1999

Campylobacter jejuni-stimulated secretion of interleukin-8 by INT407 cells.

Incubation of INT407 cells with various clinical isolates of Campylobacter jejuni resulted in secretion of interleukin-8 (IL-8) at levels ranging from 96 to 554 pg/ml at 24 h. The strains which produced the highest levels of IL-8 secretion were 81-176 and BT44. Induction of IL-8 secretion required live cells of 81-176 and was dependent on de novo protein synthesis. Site-specific mutants of 81-176, which were previously shown to be defective in adherence and invasion, resulted in reduced levels of secretion of IL-8, and cheY mutants of strains 81-176 and 749, which are hyperadherent and hyperinvasive, resulted in higher levels of IL-8 secretion. Another mutant of 81-176, which adheres at about 43% of the wild-type levels but is noninvasive, also showed marked reduction in IL-8 levels, suggesting that invasion is necessary for high levels of IL-8 secretion. When gentamicin was added to INT407 cells at 2 h after infection with 81-176, IL-8 secretion 22 h later was equivalent to that of controls without gentamicin, suggesting that the events which trigger induction and release of IL-8 occur early in the interactions of bacteria and eukaryotic cells.

Bacterial Adhesion↗
PubMed1999

Evaluation of a truncated recombinant flagellin subunit vaccine against Campylobacter jejuni.

A recombinant protein comprising the maltose-binding protein (MBP) of Escherichia coli fused to amino acids 5 to 337 of the FlaA flagellin of Campylobacter coli VC167 was evaluated for immunogenicity and protective efficacy against challenge by a heterologous strain of campylobacter, Campylobacter jejuni 81-176, in two murine models. The sequence of the flaA gene of strain 81-176 revealed a predicted protein which was 98.1% similar to that of VC167 FlaA over the region expressed in the fusion protein. Mice were immunized intranasally with two doses of 3 to 50 microgram of MBP-FlaA, given 8 days apart, with or without 5 microgram of the mutant E. coli heat-labile enterotoxin (LT(R192G)) as a mucosal adjuvant. The full range of MBP-FlaA doses were effective in eliciting antigen-specific serum immunoglobulin G (IgG) responses, and these responses were enhanced by adjuvant use, except in the highest dosing group. Stimulation of FlaA-specific intestinal secretory IgA (sIgA) responses required immunization with higher doses of MBP-FlaA (>/=25 microgram) or coadministration of lower doses with the adjuvant. When vaccinated mice were challenged intranasally 26 days after immunization, the best protection was seen in animals given 50 microgram of MBP-FlaA plus LT(R192G). The protective efficacies of this dose against disease symptoms and intestinal colonization were 81.1 and 84%, respectively. When mice which had been immunized with 50 microgram of MBP-FlaA plus LT(R192G) intranasally were challenged orally with 8 x 10(10), 8 x 10(9), or 8 x 10(8) cells of strain 81-176, the protective efficacies against intestinal colonization at 7 days postinfection were 71.4, 71.4, and 100%, respectively.

Amino Acid Sequence↗
PubMed1998

Mutation in the peb1A locus of Campylobacter jejuni reduces interactions with epithelial cells and intestinal colonization of mice.

Campylobacter jejuni is one of the leading causes of bacterial diarrhea throughout the world. We previously found that PEB1 is a homolog of cluster 3 binding proteins of bacterial ABC transporters and that a C. jejuni adhesin, cell-binding factor 1 (CBF1), if not identical to, contains PEB1. A single protein migrating at approximately 27 to 28 kDa was recognized by anti-CBF1 and anti-PEB1. To determine the role that the operon encoding PEB1 plays in C. jejuni adherence, peb1A, the gene encoding PEB1, was disrupted in strain 81-176 by insertion of a kanamycin resistance gene through homologous recombination. Inactivation of this operon completely abolished expression of CBF1, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. In comparison to the wild-type strain, the mutant strain showed 50- to 100-fold less adherence to and 15-fold less invasion of epithelial cells in culture. Mouse challenge studies showed that the rate and duration of intestinal colonization by the mutant were significantly lower and shorter than with the wild-type strain. In summary, PEB1 is identical to a previously identified cell-binding factor, CBF1, in C. jejuni, and the peb1A locus plays an important role in epithelial cell interactions and in intestinal colonization in a mouse model.

Animals↗
PubMed1997

Standardization of measurement of immunoglobulin-secreting cells in human peripheral circulation.

A sensitive, and at times the most sensitive, measurement of human vaccine immunogenicity is enumeration of antibody-secreting cells (ASC) in peripheral blood. However, this assay, which is inherently capable of measurement of the absolute number of antigen-specific ASC, is not standardized. Thus, quantitative comparison of results between laboratories is not currently possible. To address this issue, isotype-specific ASC were enumerated from paired fresh and cryopreserved mononuclear cell (MNC) preparations from healthy adult volunteers resident in either the United States (US group) or Egypt (EG group). Analysis of fresh cells from US volunteers revealed mean numbers of ASC per 10(6) MNC of 617, 7,738, and 868 for immunoglobulin M (IgM), IgG, and IgA, respectively, whereas EG volunteers had 2,086, 7,580, and 1,677 ASC/10(6) MNC for the respective isotypes. Cryopreservation resulted in a slight reduction in group mean IgM, IgG, and IgA ASC (maximum reduction in group mean, 14%), but in no instance were results obtained with cryopreserved cells significantly lower than those obtained with fresh cells. To determine if cryopreservation affected the number of bacterial antigen-specific ASC detected, cells from a group of US adult volunteers who received a single oral dose of a mutated Escherichia coli heat-labile enterotoxin (LT(R192G)) were tested. There was no significant difference (P > 0.05) in the number of antigen-specific IgA or IgG ASC detected between fresh and cryopreserved MNC. The results support the views that ASC assays can be standardized to yield quantitative results and that the methodology can be changed to make the test more practical.

Adult↗
PubMed1997

Systemic sepsis following hemorrhagic shock: alleviation with oral interleukin-6.

Gut-origin sepsis is a serious medical complication of military injuries following hemorrhage. Splanchnic ischemia induces intestinal necrosis leading to systemic bacteremia. Rat and mouse models of hemorrhagic shock were used to investigate bacterial translocation from the gut. Orally administered ameliorative treatments using the cytokine interleukin-6 (IL-6) were able to reduce or eliminate sepsis following hemorrhage. To mimic battlefield wounds and hemorrhage, anesthetized mice were bled from the femoral artery, held at a mean arterial blood pressure of 35 mm Hg for 1 hour, and then resuscitated with shed blood and 2-fold volume lactated Ringer's solution. Anesthetized rats were bled from the carotid artery at a rate of 15 ml/kg at 1 ml/minute. Bacteriological cultures of livers and mesenteric lymph nodes from hemorrhaged animals given recombinant IL-6 had significantly fewer colonies per gram of tissue than saline-fed controls. 125I-labeled IL-6 remained in the gut for up to 6 hours giving regional protection, whereas labeled interleukin-2 was disseminated throughout the body in the same time. In vivo and vitro studies of IL-6 showed that long incubations with high doses of trypsin, chymotrypsin, or intestinal contents were necessary to inactivate the bioactivity of this cytokine. Electron microscopy showed that epithelial cells from hemorrhaged mice fed saline had sparse or missing villi and vacuolated cytoplasm. Epithelial cells from control mice or mice hemorrhaged and fed cytokine appeared completely normal. Oral administration of IL-6 on the battlefield may be an important treatment for the prevention of sepsis following hemorrhage.

Administration, Oral↗
PubMed1996

Murine intranasal challenge model for the study of Campylobacter pathogenesis and immunity.

Campylobacter jejuni infection of mice initiated by intranasal administration was investigated as a potential model for studies of pathogenesis and immunity. By using a standard challenge (5 x 10(9) CFU), C. jejuni 81-176 was more virulent for BALB/c (72% mortality) than for C3H/Hej (50%), CBA/CAJ (30%), or C58/J (0%). Intranasal challenge of BALB/c was used to compare the relative virulence of three reference strains; C.jejuni 81-176 was more virulent (killing 83% of challenged mice) than C. jejuni HC (0%) or C. coli VC-167 (0%). The course of intranasally initiated C. jejuni 81-176 infection in BALB/c was determined. C. jejuni was recovered from the lungs, intestinal tract, liver, and spleen at 4 h after challenge, the first interval evaluated. After this initial interval, three distinct patterns of infection were recognized: (i) a progressive decline in number of C. jejuni CFU (stomach, blood, lungs), (ii) decline followed by a second peak in the number of organisms recovered at 2 or 3 days postchallenge (intestine, liver, mesenteric lymph nodes), and (iii) persistence of approximately the same number of C.jejuni CFU during the course of the experiment (spleen). Intranasally induced infection initiated with a sublethal number of bacteria or intranasal immunization with killed Campylobacter preparations resulted in both the generation of Campylobacter antigen-specific immune responses and an acquired resistance to homologous rechallenge. The model was used to evaluate the relative virulence of nine low-in vitro-passage (no more than five passages) isolates of C. jejuni species from patients with diarrhea. The patient isolates were differentially virulent for mice; one killed all exposed mice, three were avirulent (no deaths) and the remainder showed an intermediate virulence, killing 17 to 33%. Mouse virulence of Campylobacter strains showed a trend toward isolates originating from individuals with watery diarrhea; however, no association was found between mouse virulence and other signs or symptoms. There were no observed relationships between mouse virulence and bacterial Lior serotype or Fla polymorphic group. Intranasal challenge of BALB/c with C. jejuni is a useful model for the study of infection and vaccination-acquired immunity to this agent.

Animals↗
PubMed1995

Safety and immunogenicity of a prototype oral whole-cell killed Campylobacter vaccine administered with a mucosal adjuvant in non-human primates.

The safety and immunogenicity of two prototype oral Campylobacter killed whole-cell (CWC) vaccines were tested in rhesus monkeys. Animals were immunized with a primary two-dose series (days 0 and 14) of vaccine consisting of CWC (10(10) particles/dose) given alone or in combination with 0.5-1000 micrograms of the heat-labile enterotoxin of Escherichia coli as an oral adjuvant (OA). A booster vaccination, 4 weeks after primary immunization, was given to animals receiving CWC alone or supplemented with 0.5, 5 or 50 micrograms of OA. Both CWC and CWC-OA were well tolerated, with no adverse side-effects noted. Campylobacter-specific as well as adjuvant-specific antibody-secreting cells (ASCs) were determined in peripheral blood collected 7 days after each vaccine dose. Campylobacter-specific IgA ASC responses were enhanced by OA in a dose-dependent manner (p = 0.025), while IgG ASC responses were not. Seroconversions (both IgA and IgG) to Campylobacter antigens were also enhanced in monkeys receiving adjuvanted vaccine. No significant booster vaccination effect was observed in circulating ASCs in any of the immunization groups. In vitro T-cell proliferative responses to Campylobacter jejuni antigens were somewhat enhanced in both the CWC and CWC-OA immunization groups. These results demonstrate that CWC-OA is safe and superior to CWC alone in its ability to stimulate both local and systemic Campylobacter-specific IgA and IgG responses in primates and they support its further evaluation in human clinical studies.

Adjuvants, Immunologic↗
PubMed1995

Immunogenicity and protective efficacy of a prototype Campylobacter killed whole-cell vaccine in mice.

The immunogenicity and efficacy of an experimental inactivated Campylobacter jejuni whole-cell (CWC) vaccine were evaluated in mice. Mice were orally immunized in a three-dose primary series (48-h intervals) at doses of 10(5), 10(7), or 10(9) CWC vaccine particles alone or in combination with 25 micrograms of a mucosal adjuvant, the heat-labile enterotoxin of Escherichia coli (LT). The comparative immunogenicities of both formulations were assessed on the basis of the generation of antigen-specific antibodies in serum and intestinal secretions, and efficacy was determined by measuring the degrees of protection afforded against intestinal colonization and systemic dissemination of challenge organisms. Campylobacter-specific intestinal immunoglobulin (Ig) A responses were dependent on the use of LT, whereas IgA and IgG responses in serum were not. Colonization resistance was induced over a broad range of vaccine doses when LT was included. However, only the highest dose of CWC alone gave comparable levels of protection. Both formulations provided equivalent protection against systemic spread of challenge organisms. These results indicate that both whole-cell vaccine formulations deserve further evaluation as candidate vaccines and also highlight the potential value of mucosal adjuvants, like LT, in enteric vaccine development.

Animals↗
PubMed1995

Characteristics of Shigella sonnei infection of volunteers: signs, symptoms, immune responses, changes in selected cytokines and acute-phase substances.

Shigella sonnei infection resulting from oral administration of 500 colony-forming units was followed in 11 volunteers with the objective of studying the immune response and pathogenesis. Characterization of infection included recording of signs and symptoms, excretion of S. sonnei in stool, measurement of humoral tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), interferon-gamma (IFN-gamma), C-reactive protein, IL-2 receptor, soluble CD8, antibody-antigen complexes, and endotoxin. Measurements were also made of the immune response including lymphocytes secreting antibody to S. sonnei O antigen and serum antibody to this antigen. Six of the volunteers developed typical shigellosis with excretion of bacteria in stool and systemic signs and symptoms, three excreted bacteria but did not show illness, and two showed no evidence of infection or illness. Shigellosis was characterized by excretion in stool of S. sonnei beginning on average 1.3 days after ingestion. Excretion of S. sonnei (mean of time of the first positive cultures) was followed in sequence by the onset of increases in TNF-alpha (10 hr), liquid stools (14 hr), fever and dysentery (18 hr), IFN-gamma (22 hr), and C-reactive protein (34 hr). A S. sonnei-specific immune response was demonstrated somewhat later, between days 4 and 7 postinfection by antibody-secreting cells, and between days 7 and 14 postinfection by humoral antibody. Shigellosis was not associated with increased humoral IL-1 beta, endotoxin, or antigen-antibody complexes.

Acute-Phase Proteins↗
PubMed1993

An improved model for the examination of biological effects of locally administered cytokines.

Cytokines incorporated into agarose blocks and implanted subcutaneously into mice establish an in vivo gradient which can be used to mimic a local inflammatory process. We have developed a model in which cellular influx into cytokine impregnated blocks parallels the normal cellular reaction to infections or wounds. Agarose blocks containing supernatants from ConA activated rat spleen cells attracted neutrophils within 4 h. These cells were followed by lymphocytes and macrophages in 24 h. Flow cytometry analysis of lymphoid cells on day 1 revealed that 38% were Ig+ (B cell marker), 60% MAC-2,3+ and 20% Thy 1.2+ of which only a small fraction were expressing CD4 on their surface. These numbers changed with time following implantation of the blocks. Initially, isolated adherent cells (macrophages) were resting, with low phagocytic activity. Cells isolated from blocks at later time points were activated, as evidenced by their increased ability to ingest fluoresceinated beads. The secretion patterns of cells trafficking to murine rIL-1 containing agarose blocks were examined. TNF, IL-6 and antibody secreting cells were found. No IL-2 was detected at any time. We believe that this model will be of value in studies of local actions of cytokines.

Animals↗
PubMed1993

Activation and enhanced contact of human T-lymphocytes with autologous red blood cells are required for their stable adherence at 37 degrees.

The adherence of human red blood cells (RBC) to autologous T-cells does not occur in the body, and in vitro is elicited at 4 degrees. Autologous E-rosetting at 37 degrees has not previously been described. In this work, lymphocyte-RBC adherence has been studied in mixed leukocyte-RBC cultures and in whole blood from healthy donors. Vital, cytochemical and electron microscopic studies have shown that T-cells may form stable E-rosettes with autologous RBC at 37 degrees. As in the previously reported cold-dependent reversible rosetting, stable rosetting is mediated by the erythrocyte LFA3 and lymphocyte CD2 molecules. Uniquely, this phenomenon requires both T-cell activation and an enhanced contact between the T-cell and RBC membranes. These requirements were met by exposure of cell cultures to: (1) PHAE, the erythroagglutinating component of PHAP, or (2) to either non-erythroagglutinating mitogens, PHAL, Con A, OKT3 or SEA, or to antigens of typhus group rickettsiae or salmonellae, provided that the RBC membrane was desialyted. Cultures derived from individuals seropositive to rickettsiae or vaccinated with salmonellae demonstrated the adherence phenomenon after antigen exposure when neuraminidase was present in the culture medium. The system 2 described here can be used as a diagnostic tool for defining activated T-cells and T-cell clones with the memory to antigens capable of inducing cell-mediated immunity.

Cell Adhesion↗
PubMed1993

Modulation of mucosal immunity against Campylobacter jejuni by orally administered cytokines.

The effect of oral recombinant interleukin (rIL) treatment on the course of Campylobacter jejuni infection and the development of mucosal immunity in mice was investigated. rIL-2, rIL-5, and rIL-6 were administered to mice at 24 and 6 h before infection and at 0, 24, and 48 h after infection with C. jejuni HC, and the subsequent development of an immune response and intestinal colonization resistance were determined. In this model, orally administered cytokines retained their biological activities with no apparent side effects. Following infection, initial bacterial counts in fecal samples collected from cytokine-treated and untreated mice were similar. However, within 48 h of infection a greater than 3-log-unit reduction in the number of C. jejuni shed in the feces was found for rIL-6-treated animals. Colonization levels were similarly reduced in rIL-5-treated mice, although the rate of clearance was somewhat slower. In contrast, rIL-2 treatment had no significant effect on colonization levels compared with that in controls. Oral rIL-6 treatment was also associated with enhanced intestinal and systemic Campylobacter-specific immunoglobulin A responses compared with those observed in either rIL-5- or rIL-2-treated animals. Upon rechallenge, initial colonization in all cytokine-treated groups was approximately 2 log units lower than that in controls. However, local infection was controlled only in rIL-2-treated mice over time. rIL-5 and rIL-6 treatment had only a marginal effect on colonization resistance following rechallenge. On the basis of these results, it appears that rIL-5 or rIL-6 may function to modulate the induction and/or expression of anti-C. jejuni immunity through different mechanisms.

Adjuvants, Immunologic↗
PubMed1993

Vertical transmission of West Nile virus by Culex and Aedes species mosquitoes.

Experiments were conducted to determine whether West Nile (WN) virus was transmitted vertically by colonized strains of Aedes albopictus, Ae. aegypti, and Culex tritaeniorhynchus. Female mosquitoes were infected by intrathoracic inoculation with WN virus, and the F1 progeny were tested for virus by the fluorescence antibody technique and the newborn mouse assay. Each of the three mosquito species transmitted WN virus to F1 adults derived from immature forms reared at 26 degrees C. The minimal filial infection rate (MFIR) ranged from 1:124 to 1:138 for Ae. albopictus, from 1:62 to 1:172 for Ae. aegypti, and from 1:325 to 1:859 for Cx. tritaeniorhynchus. The MFIR for Cx. tritaeniorhynchus reared at 20 degrees C was 1:213 for larvae and 1:390 for pupae, and 1:208 for larvae and 1:554 for pupae reared at 26 degrees C. These data are the first reported evidence of vertical transmission of WN virus by mosquitoes, and therefore warrant further studies to determine whether vertical transmission occurs among WN viral-infected mosquitoes in nature.

Aedes↗
PubMed1992

Plasmodium falciparum: in vitro characterization and human infectivity of a cloned line.

The culture-adapted NF54 isolate of Plasmodium falciparum was subjected in vitro to three sequential limiting dilution titrations and the resulting clone was given the designation CVD1. DNA sequence analysis of the gene encoding the circumsporozoite (CS) protein revealed differences between CVD1 and the published NF54 CS gene. CVD1 had 1191 bp, 397 amino acids, and 42 repeat units while NF54 had 1218 bp, 405 amino acids, and 44 repeat units. The CVD1 clone was more sensitive to chloroquine than was the parental line, in vitro. Anopheles stephensi mosquitoes were infected equally by the cloned and uncloned parasites. Volunteers were readily infected by NF54 and CVD1 following infectious mosquito bites. The availability of a well-characterized, chloroquine-sensitive clone which safety infects humans should facilitate performance of experimental challenge studies to assess vaccine efficacy.

Amino Acid Sequence↗
PubMed1991

Immunogenicity of Salmonella typhi Ty21a vaccine for young children.

An attenuated Salmonella typhi Ty21a vaccine was administered to 18 infants and toddlers (less than or equal to 24 months old) to determine its safety and immunogenicity. The vaccination (10(9) CFU per dose, three doses) was well tolerated. However, after the vaccination there was no evidence of a humoral or cellular immune response to S. typhi. The vaccine used was known to be immunogenic for older children and adults. The results support the view that the immunogenicity of Ty21a is age dependent.

Administration, Oral↗