The mechanism of action of anti-lymphocyte serum. Studies of antibody eluate.

Studies designed to gain insight into the mechanism of action of the active component of antilymphocyte serum were carried out using an antibody eluate prepared from the IgG fraction of anti-lymphocyte serum by absorption and subsequent elution from thymocyte membrane. The resulting antibody eluate was labeled with radionuclide tracer to determine the fate of the antibody in vivo. The result indicated that anti-lymphocytic antibodies are eliminated from recipients extremely rapidly. The mechanism for this rapid clearance appears to depend upon the absorption of antibody molecules onto lymphocyte surfaces and the subsequent clearing and degradation of the antibody-lymphocyte complexes by the reticuloendothelial system. Distribution studies confirm that the major site of antibody-lymphocyte interaction occurs in the periphery with relatively little penetration of antibody within lymphoid organs. Radioautographic studies showed that the pattern of localization within lymphoid and other organs is confined to rather specific areas. These observations are believed to offer strong support for the notion that anti-lymphocyte serum achieves its immunosuppressive effect by bringing about a selective ablation of the population of recirculating lymphocytes.

The distribution of 51Cr-labeled lymphocytes into antigen-stimulated mice. Lymphocyte trapping.

The localization of syngeneic (51)Cr-labeled lymph node cells was investigated in CBA/J mice previously challenged with sheep erythrocytes, Salmonella H antigen, keyhole limpet hemocyanin, C57BL/6J skin, or rat skin. The effect of time, dose, and route of antigen administration on lymphocyte migration was studied in both primary and secondary responses. When the distribution pattern of lymphocytes was examined after 20-24 hr, it was found that increased localization of labeled cells occurred in spleen after intravenous or intraperitoneal antigen injection, and in draining lymph nodes after subcutaneous antigen injection or skin grafting. Increased localization (trapping) of lymphocytes was antigen dose dependent and could be demonstrated when 1-6 hr had elapsed between intravenous antigen administration, or when 24 hr had elapsed between subcutaneous antigen administration and intravenous cell infusion. Trapping was transient, lasting approximately 24 hr. Maximal trapping of lymphocytes in the draining nodes occurred 9 days after skin grafting in the first-set allograft response, and 3 days after grafting in the second-set allograft and first-set xenograft responses. The cell type trapped, the specificity and mechanism of action of the trap, and the role of lymphocyte trapping in the initiation of immune responses are discussed.

Histopathological effects in mice of heterologous antilymphocyte serum.

The effects of heterologous rabbit anti-mouse lymphocyte antiserum on the morphology of lymphoid and other tissues was investigated in CBA mice. The lymphoid tissues exhibited characteristic changes specific for ALS treatment, which were an invariable accompaniment to its immunosuppressive effects. These consisted of peripheral lymphopenia occurring at some time during a course of ALS treatment and persistent depletion of small lymphocytes in lymph node paracortical areas and splenic follicular periarteriolar zones. The thymic histology was generally well preserved. It is suggested that the relevant lesions reflect a rapid depletion of the pool of recirculating lymphocytes, possibly by a primary cytotoxic effect exerted on cells peripheral to lymphoid tissue. Other histologic features attendant to the administration of ALS were accounted for as consequences of immunization of ALS recipients to rabbit serum constituents or by the deleterious effects of antibodies directed against tissues other than lymphoid cells.

Immunological reactivity towards chondrocytes in rat and man: relevance to autoimmune arthritis.

Immunological investigation of articular chondrocytes obtained from rat and man have shown the presence of unique differentiation antigens on the cell surface demonstrated by poly- or monoclonal antibodies in both species, and by the analysis of T cell reactivity in the rat. Both species of chondrocytes express Class I antigens in common with all nucleated mammalian cells and, in man, individual specificities of the MHC A, B, and C locus can be identified using standard histocompatibility testing. Class II antigens are strongly expressed in the rat but are expressed poorly in the human specimens we have analyzed. This finding is at variance with the reports of others and may depend upon the antisera we have used or the diseased state of our patient donors. In the rat, T cell reactivity to chondrocyte antigens is strong and can be demonstrated in both proliferation and cytotoxic assay. Moreover, syngeneic reactivity is present in naive animals, suggesting that rats are not tolerant of their own CSDA. The cross-reactivity found on analysis of cytotoxic killing suggests a sharing of differentiation antigens amongst the different strains of rats and possibly a limited polymorphism for this system. In man, conventional assays for T cell reactivity are hampered by the presence of a soluble inhibitor of lymphocyte proliferation released by chondrocytes and as yet unidentified. The poor representation of Class II antigens on our chondrocyte specimens may further contribute to the difficulty in producing proliferation. On the other hand, early success is reported in finding a significant number of T cell clones isolated from the inflammatory membrane of patients with rheumatoid arthritis, which respond to chondrocyte antigens. The possibility that these antigens may play a role in the pathogenesis of inflammatory arthritis may be more readily explored by exploring these approaches.