A.M. Attallah

Natural killer cells (NK) and antibody-dependent cell-mediated cytotoxicity (ADCC) components of Schistosoma mansoni infection

Schistosoma mansoni cercariae were used to infect CBA-J mice, a strain characterized by possessing a high level of NK cells. 4 days after infection with cercariae, the natural cytotoxic capacity of these mice, as measured by NK and ADCC, reached a peak level of enhancement significantly greater than that of uninfected controls. Infection by this parasite appears to activate natural cell-mediated immune defense systems. Further observation of the pattern of response of NK and ADCC effector cells to infection by cercariae may reveal important information regarding the inherent immunity to the schistosome infection.

Differential Effects of Interferon on the MHC Expression of Human Lymphocytes

HLA antigens are the principal serologically detectable products of the major histocompatibility complex (MHC), and they function as targets for antibody-mediated and cell-mediated cytolysis. Anti-HLA sera were used in a quantitative absorption procedure to study the effect of interferon (IF) treatment on HLA expression. This study was undertaken since IF has been shown to play an important role in the regulation of cell division and function. We found that IF enhanced the expression of HLA antigens on human peripheral blood lymphocytes by 8-fold. This increase in HLA expression was specific for both the HLA-A and HLA-B regions of the MHC. There was no increase in the expression of the Ia region after IF treatment as opposed to the HLA region. Since IF is an antiviral agent and it also enhances the expression the HLA-A and HLA-B regions, it may be involved in the elimination of virus-infected cells by A and B identical effector cells.

Interferon enhanced human natural killer and antibody-dependent cell-mediated cytotoxic activity

Preincubation of normal human lymphocytes with human interferon for 18-24 h at 37 degrees C resulted in an increase of the activity of both natural killer (NK) cells and antibody-mediated cytotoxic cells (ADCC). The human myeloid line, K-562, which is highly susceptible to NK cells, was employed. ADCC was assessed with antibody-coated chick erythrocytes as targets. NK cells and ADCC were detected in a 4-hour 51Cr release assay. The magnitude of the enhancement was proportionate to the amount of interferon used in preincubation of the effector cells. Preincubation of tumor-target cells with interferon does not increase their susceptibility or resistance to lysis. The major effect of interferon on the cellular metabolism of the tumor-target cell is inhibition of DNA synthesis, but no direct cytotoxic effect was detected. Our findings may be important in understanding the mode of action of interferon in increasing host resistance to a variety of pathogens and tumors. This may be accomplished by inhibiting the growth of the tumor while simultaneously enhancing the natural killing mechanism for immunosurveillance.

Effect of the New Immunosuppressive Agent, Cyclosporin-A, on Natural Killer Cell and Antibody-Dependent Cell-Mediated Cytotoxic Activity

Athymic nude mouse homozygotes (nu/nu) and the heterozygote nu/nu+ were injected intraperitoneally with 2 mg of cyclosporin-A (CS-A) twice, 72 and 1 h prior to analysis. We have found that in vivo administration of CS-A results in a significant suppression of natural killer (NK) cell and antibody-dependent cell-mediated cytotoxic (ADCC) activity which probably play an important role in tumor and graft rejection. T cells were also suppressed, in contrast, B cells were found to be immunocompetent as determined by cell proliferation and antibody-forming capacity in response to mitogens and antigens. The identity of cells mediating NK cell and ADCC activity and its relationship to T lymphocytes are also discussed.

Detection of antibody-dependent cell-mediated cytotoxicity by automated flow cytometry. Comparison to a chromium release assay and characterization of the effector cell subpopulation.

Antibody-dependent cell-mediated cytotoxicity (ADCC) against chick red blood cells (CRBC) can be detected by flow cytometric (FCM) analysis of cellular DNA content. When compared to a standard chromium release assay FCM analysis shows several advantages: (1) equivalent cytotoxicity can be detected after 1 h compared to 4 h for 51Cr; (2) equivalent cytotoxicity can be seen at a 5-fold lower effector-to-target ratio; and (3) no radiolabeling is needed. When mouse spleen cells were fractionated based on adherence to the plastic, adherent cells showed the highest ADCC by both FCM and 51Cr release.

Immunopathology of experimental Schistosoma mansoni: immunohistochemical localization of parasite antigens in the host tissue.

Schistosoma mansoni antigens play a crucial role in the induction of immunopathological processes and in modulating the host immune system. A polyclonal rabbit antiserum to an antigenic fraction of adult schistosoma worms was used to localize worm and egg antigens in tissue sections of infected mice. Most granuloma formations identified in paraffin sections of portal tracts and intestinal mucosa were vigorous with florid cellular composition, consisting of macrophages and epithelioid cells, surrounding a central nidus of S. mansoni egg. Schistosome pigments were demonstrated at the periphery of the granuloma, within sinusoidal Kupffers cells and within macrophages of intestinal mucosa. Large amounts of schistosome antigen were found sequestered in the mesenteric lymph nodes and in the spleen. A strong reaction for locally synthesized IgG was found. These findings suggest that the schistosome antigen-antibody complex found in the host lymphoreticular system plays a major role in the immunopathological process.

Is DNA Synthesis a Requisite for the Differentiation of B Lymphocytes into Immunoglobulin-Secreting Plasma Cells?

A great amount of conflicting evidence has been reported concerning the relationship between DNA synthesis and the differentiation of immunoglobulin-secreting cells. With the development of flow cytometry, it has become possible to analyze lymphocyte populations by making rapid and accurate measurements of cellular DNA content, and by estimating the fraction of cells that synthesize DNA. Application of these techniques to an in vitro culture system stimulated by the T-dependent sheep red blood cell antigen has allowed us to investigate cell division in populations of antibody-forming cells. DNA synthesis is apparently not a requisite for the differentiation of immunoglobulin-secreting cells.

Interleukin 2 Production Induced by Chemically Defined Cell Membrane Modification

We present evidence that murine spleen cells produce a T-cell growth-stimulating factor following oxidation by periodic acid (H5IO6). The identification of this factor as interleukin 2 (IL-2) is indicated by its ability to support the growth of the IL-2-dependent CT6 cell line. In addition, preliminary analysis shows that H5IO6-stimulated growth factor has biochemical properties similar to IL-2. The time course of H5IO6-induced IL-2-like production by spleen cells was determined. No growth-stimulating activity was detected after 1 h of culture. The peak of periodic acid-induced IL-2-like production was between 18 and 24 h, while the maximum 3H-thymidine incorporation in spleen cells occurred at 72 h. Flow cytometry of CT6 cells was used for cell cycle analysis and to demonstrate their stimulation by IL-2-containing supernatants. These results were in agreement with the 3H-thymidine incorporation data. Electron microscopy of CT6 cells stimulated by supernatants from concanavalin A- or H5IO6-treated spleen cells showed no differences in their morphology. Degradation of spleen cell sialic acid prior to periodic acid oxidation inhibited IL-2-like production by 84% and inhibited 3H-thymidine uptake by 80%.

Cytochemical and Ultrastructural Alteration of Leukemic Cells by a Naturally Cytotoxic Factor from Spleen

Experiments were carried out to delineate the differences in cytocidal modality of natural splenic cytotoxic factor (30,000-50,000 daltons) and cyto-A against normal and human leukemic lymphocytes in vitro. It was found that the differences in the cytocidal action effected by cyto-A and splenic isolate were as follows: (1) the killing effect of cyto-A against leukemic cells was very rapid in contrast to the slowly acting spleen factor as evaluated by cytochemical and ultrastructural studies; (2) spleen factor was not cytotoxic against normal lymphocytes in contrast to the indiscriminatory cytotoxic cyto-A.