Abstract: Previous reports have demonstrated that accessory cells function to present soluble protein antigens in association with gene products encoded within the I region of the major histocompatibility complex (MHC) to antigen-reactive T helper cells. The biochemical events that occur during antigen presentation are, however, not well-documented primarily because of the difficulties involved in purifying sufficient numbers of homogeneous antigen-presenting cells. In this paper, a number of Ia-positive B lymphocyte tumor lines are shown to be capable of presenting soluble protein antigens to antigen-reactive continuous T cell lines in an MHC-restricted fashion. The characterization of the antigen presentation function of these tumor cells indicates that the tumor cells have many of the functional antigen-presenting characteristics previously thought to be limited to macrophages. These tumor cells should provide a useful model system for determining the biochemical events that occur in antigen uptake and processing as well as for determining the potential interactions between processed antigen and Ia molecules on the plasma membrane of these antigen-presenting cells.

Abstract: The roles of Ia+ accessory cells in H-2-restricted stimulation of antigen-specific T cell proliferation were explored in an in vitro model. L-glutamic acid60-L-alanine30-L-tyrosine10-(GAT) primed BALB/c nylon wool-passed T cells were depleted of Ia+ antigen-presenting cells (APC) by treatment with monoclonal anti-Ia antibody plus complement. Such cells failed to respond to soluble GAT, or to soluble GAT in the presence of phorbol myristic acetate (PMA), which is known to stimulate production of, or replace, IL-1 in vitro. Addition of gamma-irradiated syngeneic spleen cells reconstituted the response to soluble GAT, but addition of ultraviolet (UV) light-irradiated spleen cells did not, even in the presence of PMA. Preincubation of cells with GAT for 24 hr, followed by washing, then gamma irradiation, generated a cell population able to stimulate GAT-primed T cells to proliferate. The same pulsed cells exposed to UV irradiation failed to stimulate T cell responses unless PMA was added to the cultures. The relevant cells in this UV-irradiated population are Ia+. It is concluded that a finite period of time for interaction of metabolically intact APC with antigen is required before creation of an appropriate (Ia + antigen) signal recognized by the T cell. In addition to such Ia-restricted antigen presentation, however, a 2nd nonspecific signal, again requiring metabolically active APC for elaboration, is necessary for detectable T cell activation. These studies thus define 3 separable activities of APC during the process of H-2 restricted T cell activation.

Abstract: We demonstrate that splenic adherent cells (SACs) play an active role in the presentation of H-2Kk antigen for an alloreactive cytotoxic T-lymphocyte (CTL) response. If antigen is incubated with SACs for 12 hr, they will provide maximal stimulation and present the antigen in the context of their Ia molecules. UV irradiation of these SACs, prior to the 12-hr incubation with H-2Kk antigen, abrogates this stimulatory capacity. Macrophage-bound antigen is not sufficient for stimulation of a response; a second signal is required as well, that, in our system, is provided by phorbol myristic acetate. The SACs are involved in the activation of helper T cells; however, they are not required for presentation of antigen to the precytotoxic T-lymphocyte, which requires two signals for activation, one provided by antigen and the other by a T-cell-derived helper factor.

Abstract: In the chicken MHC there exist two regions, designated F and G, which were separated by crossing-over. The F region contains genes controlling all functions characteristic of the MHC. So far only one gene has been assigned to the G region and it is responsible for the presence of an RBC antigen. When cross-immunizing animals of the congenic lines CB and CC with erythrocytes, we have found that both F- and G-specific antibodies were produced. By using the recombinant haplotypes Br1 and Br2 we were able to dissociate the F from the G antigen and immunize with them separately. It was found that production of F antibodies required the copresence of the G antigen, whereas G antibodies were formed regardless of the presence of absence of the F-region antigen. It could be demonstrated that a prerequisite of the role of the G antigen with respect to the F antigen was the localization of both antigens on the same erythrocyte. Possible mechanisms underlying this phenomenon are discussed.

Abstract: This study was undertaken to investigate the nature of the immunogenic moiety recognized by the human T cell which proliferates in response to tetanus toxoid (TT) antigen. Immunosorbent-purified anti-TT IgG antibodies failed, even when added in great excess, to inhibit T cell proliferation in response to TT. Urea-denatured (UD) TT antigen containing less than 1% native TT, as assessed by its reactivity with antibodies raised against native TT, triggered proliferation in T cells to an extent equal to that seen with native TT. The proliferative response to UDTT was seen only in T cells obtained from donors immune to TT and was inhibited by antisera to DRw antigens of the cell donor. T cells responding to TT and to UDTT essentially overlapped because exposure to 5'-bromo-2-deoxyuridine and light of T cells prestimulated with TT or UDTT abolished the specific response to both forms of the TT antigen but not to phytohemagglutinin or to Monilia antigen. It is concluded that proliferating human T cells recognize determinants which differ from those that elicit an antibody response and which may arise as a result of antigen processing by macrophages. The implications of these present results on the nature of the human T cell receptor for antigen are discussed.

Abstract: Male-specific H-Y antigen may be defined by graft rejection, killer cell action or antibodies. Most commonly H-Y antigen is detected in assays using H-Y antisera. In these tests errors may arise from various causes: 1) Auto- and heteroantibodies cross-reacting with target cells. 2) Restriction phenomena. 3) MHC-dependent modification of the amount of H-Y antigen present on different tissues. 4) Modification of cell surface antigens by bacteria or viruses. Regarding the third definition of H-Y antigen, four different “states” can be distinguished in the mammalian male. H-Y occurs (1) as an integral part of the plasma membrane; (2) unspecifically attached to the membrane of human erythrocytes; (3) free in solution; (4) bound to its gonad-specific receptor. Redistribution experiments suggest that H-Y and β 2-m are associated on the cell membrane. Coredistribution is not found of H-Y and MHC antigens. An antibody blocking technique demonstrates association of H-Y and H-2D antigens on unfixed lymphoid, but not on testicular cells. Human erythrocytes lacking β 2-m do not integrate H-Y antigen into the cell membrane. Male erythrocytes, however, absorb H-Y antigen from the serum. The origin of H-Y antigen in the serum is not clear. It may be shed from cell membranes, derive from the testis which actively secretes H-Y antigen, or both. H-Y antigen is bound by a gonad-specific receptor. This receptor is present in the gonads of both sexes. H-Y antigen is supposed to mediate testis differentiation via this receptor. Reaggregation experiments in vitro using dissociated gonads of the newborn rat demonstrate that ovarian cells reorganize into testicular structures in the presence of H-Y antigen. The assumption cannot be confirmed that addition of H-Y antiserum to testicular cells results in ovarian structures. This finding, however, does not conflict with the view that H-Y antigen is involved in testis differentiation, e.g. by inducing testis cell-specific functions via the gonad-specific receptor.

Abstract: The significance of the dichotomy of MHC antigens was investigated. It was determined that primed helpers directed against allogeneic class 1 antigens (K and D in the mouse) were not restricted to syngeneic class 2 antigens (I in the mouse). Furthermore, the generation of helper T cell-replacing factor by stimulation with K or D antigens was not blocked by Ia antibodies that were effective in blocking the same factors generated in response to I region MHC antigens. It is concluded that class 2 antigens are not recognized during the response of helpers to class 1 antigens, and it is suggested that class 1 and class 2 molecules can perform reciprocal functions.

Abstract: SUMMARY AND CONCLUSIONS (1) Chimeras of the type (P, X P2)Fi-Pi have a fragile state of T cell tolerance toP2 antigens. Though no ongoing response to P2 antigens can be detected in thespleen at the time of its removal, anti-P2 MHC responses can be provoked invitro (Tc cell generation), or in vivo (skin graft rejection). These results imply thatanti-P2 T cell precursors are present in these mice but are usually suppressed.If the idiotypes of anti-P2 T cells crossreact with those of anti-P2 + X T cells,then this could contribute to the observed bias of H-2 restricted responses to Rantigens of Pi type,(2) Lymphomyeloid cells of (PiXP2)Fi origin that repopulate the lymphoidtissues of irradiated Pi mice can apparently express less P2 MHC antigens thannormal Fi cells. If this contributes to the fragile state of T cell tolerance to P2antigens in the secondary lymphoid tissues of chimeras, it implies that inductionor maintenance of self tolerance to MHC antigens is quantitatively dependentupon MHC antigen expression,(3) The amount of H-2 antigen expressed on lymphomyeloid cells apparentlydepends not only on the genotype of the stem cells from which they are derived,but on the environment in which lymphomyeloid differentiation takes place.

Abstract: Summary Two patients with Wiskott-Aldrich syndrome were studied immunologically and biochemically. The same immunological abnormalities were found in these patients as described in the previous cases. Futher, the expression of IgG-Fc receptor on the surface of monocytes was poor and anti-D coated human erythrocytes were less phagocytized by these cells from the patients than by control cells. The hexokinase activity was low in mononuclear cells (30% of the control mean) but normal in erythrocytes. It was suggested that a disturbance of the energy metabolism may affect the antigen processing mechanism and the afferent limb of immunity in the immunocompetent cells in this disease.

Abstract: We have investigated the cellular and antigenic requirements for incubation of secondary proliferative responses by human T lymphocytes. Two distinct properties of antigen-presenting peripheral blood mononuclear cells were studied: (a) the ability for appropriate cell surface constituents to construct an immunogenic moiety, and (b) the ability to present similar antigenic determinants when they are not covalently bound. Only Ia+ hapten-modified cells were effective stimulators. In contrast, both Ia+ and Ia- cell sonicates could stimulate secondary proliferative responses, but only in the presence of an accessory cell. This accessory cell was present in Ia+ macrophage, but not in Ia+ non-T lymphocyte, preparations. In contrast, macrophages or soluble factors produced by macrophages were not required for primed T cells to undergo hapten-specific proliferation in response to hapten-modified Ia+ stimulator cells. Thus, although all Ia+ cells tested can stimulate primed cells to proliferate, not all Ia+ cells can function as accessory cells for responses to sonicates. This may reflect the unique ability of a subpopulation(s) of Ia+ cells to bind or process sonicates or soluble antigens for appropriate recognition by primed T cells.

Abstract: The mechanism of macrophage-antigen handling was studied using a system that involves the quantitation of the antigen-specific binding of Listeria monocytogenes-immune T cells to macrophages. Specific T cells did not bind to native antigen. Because the specific binding of T cells to macrophages could be measured during a short (5- to 15-min) interaction, it was possible to follow the temporal development of a T cell-binding substrate with increasing time of antigen-macrophage interaction. In contrast to the rapid (5-min) uptake of Listeria by macrophages, the development of T cell-binding ability required a 30- and 60-min period of antigen-macrophage interaction. During this processing period, Listeria organisms bound to the macrophage surface were ingested and partially catabolized. Unlike antigen uptake, antigen processing was a temperature-dependent and energy-requiring event. Although macrophages treated with paraformaldehyde before antigen processing did not develop T cell-binding activity, macrophages treated with paraformaldehyde after a 60-min antigen-processing period retained T cell-binding ability. The kinetics of antigen catabolism correlated with antigen processing, and inhibition of antigen catabolism was associated with a corresponding inhibition of antigen processing for T cell binding. Anti-Ia antibodies had no effect on Listeria uptake of catabolism. These results supply direct evidence for a macrophage-antigen processing event relevant to T cell recognition of antigen.