The in vivo and in vitro effectiveness of several monoclonal antimouse T and B cell antibodies, of anti-Th-1 and of Iak serum, as well as of ATG were compared. The parameters were prolongation of skin graft survival, prevention of graft-versus-host disease (GVHD), antibody and primary and secondary plaque formation against sheep redblood cells (RBCs), and T cell depletion of lymphoid tissues. In general, in vitro effectiveness of the monoclonal antibodies exceeded their in vivo effectiveness. Skin graft survival was prolonged by ATG, but not by monoclonal anti-T, or anti-T plus anti-B antibody. GVHD was prevented by in vitro incubation of donor bone marrow with monoclonal anti-Th-1, but in vivo treatment of marrow donors was ineffective. Treatment with ATG was successful. Anti Iak antibody blocked plaque formation by spleen cells incubated with sheep RBCs, but had no effect on secondary plaque formation when given in vivo. Neither was there any in vivo effect of anti-Iak or anti-Th-1 on antisheep RBC agglutinin formation. ATG was effective in both of these assays, although its cytotoxic and complement-fixing titer did not exceed that of anti-Th-1 or anti-Iak. Although anti-Th-1 was cleared more rapidly from the serum of mice expressing the corresponding Th-1 alloantigen, than from mice with the noncorresponding alloantigen and although anti-Th-1 was shown to bind to the T cell areas of the lymphoid tissue, it did not--unlike ATG--deplete these areas of T cells. Possible reasons for the difference in effectiveness of in vitro and in vivo application of these monoclonal antibodies are discussed.

Fifteen monoclonal antibodies against different T-cell antigens were studied by immunohistochemistry in thymus, fetal thymus, fetal liver, palatine tonsils, and a few T-cell lymphomas. OKT 9 was identified as reacting with hemopoietic stem or precursor cells in fetal liver as well as with early B-determined lymphocytes in tonsillar germinal centres. OKT 10 labelled lymphocytes in thymus and surprisingly also the cytoplasm of some tonsillar cells with plasma-cell like appearance. OKT 6 and MAS 036 b reacted only with thymic cells. OKT 4, OKT 5, OKT 8, 8–11, labelled thymic cells- and portions of interfollicular cells in tonsils. OKT 3, NEI 016, NEI 015, and T 28 stained a majority of thymic cells and of tonsillar interfollicular lymphocytes. IFH-M 203, NEI 012 and 4–11 were positive with the majority of T-lymphocytes in tonsils but labelled only a few thymic cells.

The unlabeled antibody enzyme method was used to delineate the anatomical distribution of lymphocytes positive with a-MBΘ and a-MIg in tissue sections of thymus, spleen, lymph nodes and Peyer's patches of mice. The known T- and B-cell areas were established. Moreover, individual B-cells were detected in T-cell regions, especially in the thymus medulla, and in the periarteriolar section of spleen white pulp. Similarly, individual T-cells occur in B-cell areas, namely in the marginal zone of spleen white pulp, in the medullar cords of lymph nodes, and in germinal centers.

C57BL/6J mice were treated with ALS, ALG, normal rabbit serum (NRS) or IgG of the rabbit for a period of 6 days. To study the xenogeneic antigenicity of ALG and its antilymphocytic effect separately, half the mice were made tolerant to IgG of the rabbit. While a short schedule of injections of ultracentrifuged IgG induced tolerance to IgG, this tolerance was eliminated by the subsequent treatment with ALG. A prolonged injection schedule over 44 days did, however, lead to a tolerance which persisted after ALG treatment. [131I]IgG elimination proved to be a more sensitive control of tolerance than immunodiffusion. Semiquantitative cytology revealed a decline in lymphocytes, erythroblasts and megakaryocytes in the bone marrow and erythroblastosis and megakaryocytosis in the spleen. Cells of the myeloid series invariably increased in number. The effect on erythroblasts persisted after removal of contaminating haemagglutinins. ALG-treated animals intolerant to IgG had about four times more splenic plasma cells than ALG-treated mice tolerant to IgG. The 6 days' treatment with ALS reduced the absolute number of nucleated bone marrow cells by 16% and doubled the spleen indices. Under this treatment, relative and absolute cell counts revealed an ALG-induced shift of erythroblasts, megakaryocytes and perhaps also of plasma cells from the bone marrow to the spleen. The effect of NRS or IgG was similar to that of ALS or ALG but remained on a lower level. The remarkable changes in the histologic structure of the splenic follicles after ALG treatment were almost completely reversed by a prior induction of tolerance to IgG.

Es wurde die immunsuppressive Wirkung einer 6tägigen ALγG-Behandlung auf das Knochenmark ALγG-toleranter Spender an Hand der Überlebenszeit letal bestrahlter, allogener Empfänger getestet. Dabei ergab sich, daß Mäuse, die das mit ALγG behandelte Knochenmark ALγG-toleranter Tiere erhielten, eine geringere Überlebenszeit aufwiesen als Mäuse, die Knochenmark von nicht-toleranten ALγG-behandelten Mäusen bekamen (p≦0,05). Wir folgern daraus, daß sich die immunsuppressive Wirkung von ALγG aus einer lymphocytotoxischen und einer immunogenen Komponente zusammengesetzt.