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E L Chan

Publications and source records attributed to E L Chan.

48 records · Page 3Linked to original sources
PubMed1982

In vitro studies with cefotaxime: disk diffusion susceptibility tests.

Until recently two sets of conflicting interpretive criteria existed for use with the standardized 30-mug cefotaxime diffusion disk [National Committee for Clinical Laboratory Standards (NCCLS) M2-A2S, supplement 1; product information package insert for Claforan (cefotaxime sodium), edition 10/81.] The latter criteria recently were superseded by a third set which differs radically from the first two in both minimal inhibitory concentration (MIC) and zone size breakpoints. The first two sets of criteria differed mainly in the zone of inhibition diameters used to predict resistant and intermediate organisms. The accuracies of these two sets of criteria were evaluated by paired agar dilution (World Health Organization-International Collaborative Study) and disk diffusion tests (Food and Drug Administration) with 347 clinical isolates of aerobic bacteria. A total of 274 isolates (79%) were clinically susceptible by agar dilution as defined by NCCLS (MIC </=8 mug/ml) and 61, including 48 Pseudomonas spp., were of intermediate susceptibility (MIC of 16 or 32 mug/ml). Twelve were resistant (MIC >/=64 mug/ml). The original product information package insert criteria proved to be most unreliable in identification of the intermediate organisms (zone of inhibition diameters of 18 to 22 mm); only 5 were correctly predicted as being intermediate, whereas 54 were predicted as being resistant, and 2 were predicted as being susceptible. In contrast, the NCCLS criteria (zone of inhibition diameter of 15 to 22 mm) predicted 41 as being intermediate and 18 as being resistant; again, 2 were susceptible. The 12 isolates resistant to cefotaxime by agar dilution were correctly predicted to be resistant by either set of breakpoints (zone of inhibition diameter of </=14 or </=17 mm). These results suggest that the package insert criteria previously recommended for use with the 30-mug cefotaxime disk were overly conservative and required revision to bring them into agreement with NCCLS performance standards. Unfortunately however, the recent revision of the package insert criteria has further confused this issue [product information package insert for Claforan (cefotaxime sodium), edition 2/82].

Bacteria↗
PubMed1977

Immunosuppressive effects of lymphocyte (type II) and leucocyte (type I) interferon on primary antibody responses in vivo and in vitro.

We have tested the hypothesis that type II interferon (IF), released by immune lymphocytes after in vivo stimulation with tuberculin, has immunosuppressive effects. Mycobacterium bovis (BCG) infected mice injected with tuberculin showed a very intense suppression of antibody response to sheep erythrocytes. Sera containing lymphocyte IF strongly inhibited primary immune responses to sheep erythrocytes in cultures. Addition of macrophages could not counteract the in vitro immunosuppressive effects of lymphocyte IF, suggesting that the main effect is exerted directly on lymphocytes. Sendai virus-induced leucocyte (type I) IF was also shown to have suppressive effects in vivo and in vitro. However, lymphocyte IF was shown to be much more immunosuppressive than a preparation of type I interferon with equivalent antiviral potency. Thus type II IF, as a product of activated lymphocytes, may have a major immunoregulatory role.

Animals↗
PubMed1977

Expression and function of I region products on immunocompetent cells. II. I region products in T-B interaction.

The anti-Lac B precursor cells from BALB/c (H-2)d mice which survive cytotoxic treatment with anti-Iak and complement will respond to Lac-KLH in culture but require more KLH helper T cells than unselected B cell populations or B cells surviving anti-Ig killing. These findings are not explainable by the classical Poisson assumption of a constant target of T-B ionteraction. We propose a T-B interaction theory with variable Ia target on the B cell surface. The theory quantitatively predicts the observed dose response relationships, and implies that Ia molecules on B cells are cell interaction structures.

Animals↗
PubMed1977

Long-term effects of in vitro sensitization on immune reactivity of lymphocytes: generation of suppressor and helper T cells.

Mouse spleen cells were cultured for 5 days with or without HRBC. Cultured cells were 'parked' in irradiated syngeneic recipients for 3 weeks and then tested for their immunologic reactivity in vitro. We found that spleen cells from recipients of HRBC-sensitized cells (S) as well as spleen cells from recipients of control unsensitized cells (U) possessed radiosensitive suppressor and radioresistant helper activities. Suppressor activity was observed by the capacity of unirradiated S and U spleen cells to inhibit the in vitro generation of IgM and IgG PFC by spleen cells primed in vivo to HRBC or to LacKLH. Helper activity was shown by the capacity of the irradiated S and U cells to restore IgM and IgG PFC responses of in vivo primed, T-depleted spleen cells to HRBC, LacHRBC, and LacCRBC. Both suppressor and helper activities were mediated by T cells. The possibilities that immunologically specific or nonspecific mechanisms account for these phenomena are discussed.

Animals↗
PubMed1977

Expression and function of I region determinants on immunocompetent cells. I. Selective expression of I-C region determinants on immune cells.

We have examined the cytotoxic activity of anti-Iak serum and complement on various immune functions of BALB/c (H-2d) cells. Since the cytotoxic action of this antiserum on H-2d cells defines specificity Ia.7, an I-C region product, we have looked at the selective expression of this antigen. We have mainly used the in vitro anti-Lac2 response to study the cells involved in the induction and regulation of antibody. The data presented here show that Ia.7 is present on both IgM and IgG precursor B cells and in lesser amounts on plaque-forming cells. The antiserum also recognizes with less efficiency a product on specific T suppressor cells, which is possibly coded for by the adjacent I-J subregion. Both fluorescence and functional tests indicate the absence of Ia.7 on macrophages. It is also lacking on T helper cells. When we tested the antiserum on the in vitro cytotoxic responses to alloantigens, we found that neither T effector cells nor their precursors were affected.

Animals↗
PubMed1976

Coexistence of helper and suppressor activities in carrier-primed spleen cells.

Both helper and suppressor activities for an in vitro IgG anti-hapten (Lac) response to Lac-HRBC were demonstrated in the same population of carrier (HRBC)-primed spleen cells. The relative radiosensitivity of suppressor activity permitted the selective removal of suppression and the demonstration of help. Both activities appear to be T cell-dependent and antigen-specific. Dilution analysis showed that help and suppression are mediated by distinct populations of cells.

Animals↗
PubMed1973

Active suppression of immunoglobulin allotype synthesis. 3. Identification of T cells as responsible for suppression by cells from spleen, thymus, lymph node, and bone marrow.

Thymus-derived cells (T cells) that actively suppress production of IgG2a immunoglobulins carrying the Ig-1b allotype have been found in adult (SJL x BALB/c)F(1) mice exposed to anti-Ig-1b early in life. The suppression is specific for Ig-1b. The allelic product, Ig-1a, is unaffected. Spleen, lymph node, bone marrow, or thymus cells from suppressed mice suppress production of Ig-1b by syngeneic spleen cells from normal F(1) mice. When a mixture of suppressed and normal cells is transferred into lethally irradiated BALB/c mice, there is a short burst of Ig-1b production after which Ig-1b levels in the recipient fall rapidly below detectability. Pretreatment of the cells from the suppressed mice with antiserum specific for T cells (anti-Thy-1b) plus complement before mixture destroys the suppressing activity. Similar results with suppressor cells were obtained in vitro using Mishell-Dutton cultures. Mixture of spleen cells from suppressed animals with sheep erythrocyte (SRBC)-primed syngeneic normal spleen before culture suppresses Ig-1b plaque-forming cell (PFC) formation while leaving Ig-1a PFC unaffected. Treatment of the suppressed spleen with anti-Thy-1b before transfer removes the suppressing activity.

Animals↗
PubMed1972

Immunological memory in mice. 3. Memory to heterologous erythrocytes in both T cell and B cell populations and requirement for T cells in expression of B cell memory. Evidence using immunoglobulin allotype and mouse alloantigen theta markers with congenic mice.

Using anti-allotype sera and AKR anti thetaC3H sera, a requirement for two cell types has been demonstrated in the adoptive secondary response of mice to heterologous erythrocytes. The cell types have been designated B cells [precursors of plaque-forming cells (PFC)] and T cells (thymus-influenced cells, not providing precursors of detectable PFC). The in vivo indirect PFC response of spleen cells from primed mice is markedly reduced by in vitro treatment of the cells with a mixture of anti-theta serum and guinea pig serum (Anti theta + GPS). This B cell response is fully restored to control levels by thymus cells from normal mice which do not themselves provide precursors of indirect PFC. Thus memory is carried by the B cell lineage but the expression of this memory is dependent on the presence of a cell population which is sensitive to Anti theta + GPS and which is replaced functionally by unprimed T cells. When assayed for T cell activity, thoracic duct cells from specifically primed mice are better than cells from nonspecifically primed mice in restoring the B cell response of spleen cells from immunized mice. Moreover, the T cell activity of a reconstitutive cell population from primed mice is reduced by incubation with Anti theta + GPS. We conclude that memory to heterologous erythrocyte antigens is carried by the T cell lineage as well as the B cell lineage even though unprimed T cells are sufficient for expression of B cell memory.

Animals↗
PubMed1970

Cell interaction in an immune response in vitro: requirement for theta-carrying cells.

Cytotoxic antiserum to theta antigen reduces the capacity of mouse spleen cells to generate direct and indirect plaque-forming cells to sheep erythrocytes in vitro but does not affect plaque-forming cells, their precursors, or hemopoietic stem cells. The response of spleen cells treated with antiserum to theta antigen is restored by thymus cells incubated in vivo with sheep erythrocytes.

Animals↗