Cell-mediated cytotoxicity against HLA-D-region products expressed in monocytes and B lymphocytes. I. Blocking by Unlabelled cells and inhibition by antisera

Cytotoxic effector cells against HLA-D-region produts were generated in cultures with HLA-A- and B-matched, HLA-D-mismatched stimulating cells. Monocytes from unrelated donors sharing HLA-D/DR antigens with the primary stimulator were used as target cells. Lysis of target cells was inhibited by addition of unlabelled monocytes having the same HLA-D/DR antigens. Inhibition of cytotoxicity was also observed with unlabelled B cells, but T lymphocytes had little effect. The distribution of the target antigens, therefore, fits the known distribution of the products of HLA-D. In other experiments, a human alloantiserum specific for HLA-DRw3 was found to inhibit cellular cytotoxicity specific for HLA-D/DRw3. Lysis by HLA-D/DRw3-specific effector cells was not inhibited by sera against HLA-DRw2 or DRw7 or by antibodies against HLA-B8 using HLA-B8 positive, DRw3 positive targer cells. A xenogeneic serum against human Ia antigens, produced in rabbits, blocked cytotoxicity directed at DRw2, DRw3 and DRw4. These results suggest that cell-mediated cyctotoxicity was directed against HLA-D/DR or very closely associated determinants.     

Cell-mediated cytotoxicity against HLA-D-region products expressed in monocytes and B lymphocytes

Cytotoxic effector cells against HLA-D-region products were generated in cultures with HLA-A- and B-matched, HLA-D-mismatched stimulating cells. Monocytes from unrelated donors sharing HLA-D/DR antigens with the primary stimulator were used as target cells. Lysis of target cells was inhibited by addition of unlabelled monocytes having the same HLA-D/DR antigens. Inhibition of cytotoxicity was also observed with unlabelled B cells, but T lymphocytes had little effect. The distribution of the target antigens, therefore, fits the known distribution of the products ofHLA-D. In other experiments, a human alloantiserum specific for HLA-DRw3 was found to inhibit cellular cytotoxicity specific for HLA-D/DRw3. Lysis by HLA-D/DRw3-specific effector cells was not inhibited by sera against HLA-DRw2 or DRw7 or by antibodies against HLA-B8 using HLA-B8 positive, DRw3 positive target cells. A xenogeneic serum against human Ia antigens, produced in rabbits, blocked cytotoxicity directed at DRw2, DRw3 and DRw4. These results suggest that cell-mediated cyctotoxicity was directed against HLA-D/DR or very closely associated determinants.     

Inhibition of the induction of cytolytic T lymphocytes with alloantisera directed against H-2K and H-2D gene products.

Alloantisera directed at gene products of the H-2Kd or H-2Dd loci on the stimulator cell were shown to inhibit specifically the generation of cytolytic T lymphocytes to those antigens. Thus, masking the antigens of one H-2 locus on the stimulator cell inhibits the induction of CTL to products of that locus but does not inhibit the induction of CTL to antigens of another H-2 locus. Alloantisera inhibition of the induction of cytolytic T lymphocytes occurred with both normal and primed responder cells and also occurred when the stimulating antigens were on whole cells or purified plasma membrane. Absorption on the appropriate spleen cells removed the inhibitory capacity of these alloantisera.     

Antiserum inhibition of the mixed lymphocyte culture (MLC) interaction. Inhibitory effect of antibodies reactive with HLA-D-associated determinants.

Two antisera, procured by immunization within HLA-A- and HLA-B-identical and HLA-D-incompatible unrelated combinations, were cytotoxic to B lymphocytes from the immunizing donor and from persons sharing his HLA-D-incompatible phenotype(s). The sera strongly and specifically inhibited lymphocytes from these donors when used as stimulating cells in mixed lymphocyte culture (MLC) reactions, while specific responding cell inhibition was less evident. The inhibitory effect was retained in the immunoglobulin G (IgG) and the F (ab)′₂ fractions of these antisera. Inhibition was observed when the antisera were added within 48 hr after initiating the MLC. We conclude that these antisera contain antibodies reactive with structures closely associated with HLA-D determinants and that these may be human analogs of the mouse Ia antigens.     

Role of antigen-specific B cells in the induction of SRBC-specific T cell proliferation

In this study, we ask whether antigen presentation can be effected by antigen-activated B cells. Antigen-dependent in vitro proliferation of T cells from mice primed with SRBC or HoRBC occurs in the presence of B cells primed to the relevant antigen. B cells prepared from lymph nodes of mice primed with irrelevant antigens are not effective antigen-presenting cells for RBC-specific T cell proliferation over a wide range of SRBC doses. This is true even when both RBC and the antigen to which the B cells are primed are included in the culture. In contrast, B cells specific for a hapten determinant coupled to SRBC are able to support proliferation of T cells specific for SRBC determinants. We conclude from these data that antigen-specific B cells play a role in the induction of T cell proliferative responses to SRBC and HoRBC antigens. Two models are proposed: either B cells, upon antigen interaction with surface antibody, are able to act as accessory cells to induce Ia-dependent proliferation of immune T cells; or B cells augment the T cell proliferative response by secretion of antibody, leading to opsonization of the antigen for macrophage uptake and presentation.     

The presence of Ia-like determinants on a subpopulation of human T lymphocytes

By planned immunization within HLA-A-, and -B-compatible and HLA-D-disparate combinations, we have raised two antisera which are cytotoxic in complement-dependent cytotoxicity (CDC) tests with B lymphocytes, but not with T lymphocytes, from the immunizing donor and other donors sharing the immunizing HLA-D phenotype. The sera were found previously to inhibit the stimulating capacity of cells in MLC and the Fc receptor of cells producing EA rosettes, suggesting that they may detect alloantigens analogous to Ia antigens in mice. Although apparently non reactive with T cells in CDC tests and immunofluorescence, these sera were investigated further for their potential interference with some T-cell functions. After pretreatment with the appropriate antiserum and complement, the cells behaved normally as responding cells in mixed lymphocyte culture, as precursors to the cytotoxic cells in cell-mediated lympholysis, and as cells responding to the purified protein derivative (PPD). However, the response to phytohemagglutinin (PHA) was reduced at low concentrations of this mitogen, and the response to concanavalin A was strongly reduced at all concentrations, indicating that some subpopulations of human T cells also carry Ia-like specificities.     

Specific absorption of T lymphocytes committed to soluble protein antigens by incubation on antigen-pulsed macrophage monolayers.

Monolayers of macrophages (Mphi) pulsed with antigen were used as immunosorbents for T lymphocytes from guinea pigs primed to soluble protein antigens. T lymphocytes were cultured on the Mphi monolayers for 4 hr, then aspirated and reincubated on a fresh monolayer pulsed with the same antigen for a second and a third step. T lymphocytes so treated were selectively deprived of cells responding in assay for antigen-dependent proliferation against the antigen used for pulsing the absorbing monolayer, but maintained their response to other antigens. The lymphocytes adhering to the Mphi of the absorbing monolayer were capable of giving a full response to the antigen used for pulsing the Mphi of the monolyers. The proliferative response of F1 T lymphocytes to antigen in association with Mphi of either parental strain could be absorbed leaving the response to antigen in association with Mphi of the other parental strain. The absorption of the proliferative response was not inhibited by addition of excess soluble antigen to the medium of the absorption culture. Our results indicate that specific guinea pig T lymphocytes responding by proliferation to soluble protein antigens recognize and bind specifically to a complex of Ia antigen and protein antigen at the surface of the Mphi.     

Human immune responses to hapten-conjugated cells. II. The roles of autologous and allogeneic histocompatibility determinants in proliferative responses in vitro.

Proliferative responses of human lymphocytes primed in vitro to autologous TNP-cells were found to be associated with autologous D-region determinants irrespective of HLA-B locus antigens. Family studies of secondary TNP-conjugate proliferative responses demonstrated a gene dosage effect in this phenomenon. Moreover, co-culture with allogeneic cells did not affect the net TNP-conjugate proliferative responses of primed responder cells, suggesting that HLA-D region preference was due to a requirement for representation of TNP-molecules in association or combination with autologous MHC structures. Alloantigens were found to influence the sensitization of lymphocytes to autologous hapten-conjugated cells. Co-culture of allogeneic and TNP-modified autologous stimulator cells in primary cultures enhanced the secondary TNP proliferative response. Sensitization of human lymphocytes to allogeneic cells alone did not prime responses to autologous modified cells. However, priming lymphocytes to modified autologous cells potentiated responses to allogeneic cells. The data suggest a complex relationship between responses to alloantigens and modified autologous cells.     

Genetics of cell-mediated lympholysis in man.

Cell-mediated lympholysis (CML) was studied in a family containing two siblings in who genetic recombinaiton had occurred in the HLA comples. In one sibling, recombination occurred between the HLA-A locus and the HLA-B locus. In the second sibling recombination occurred between the HLA-B locus and the HLA-D locus. Strong CML activity was generated in mixed lymphocyte cultures (MLC) when stimulator and responder cells differed in HLA-A, B, and D antigens. MLC involving HLA-D differences alone did not generate CML. Weak, but definite CML activity was generated during MLC with cells differing at HLA-A and HLA-B but sharing HLA-D. HLA-B antigens were good targets for lysis in all combinations studied. HLA-A antigens were poor targets in some but not in all combinations. However, combinations where HLA-A antigens seemed to be good targets could have involved HLA-B differences due to polymorphism of HLA-B7 antigens each inherited from a different parent. HLA-D antigens did not serve as targets for lysis. In three cell experiments, excellent CML activity was generated when responder cells were stimulated by HLA-D antigens and by HLA-A and B antigens present on separate stimulator cells.     

Immune maturation of T lymphocytes: sequential changes in the functional specificity and apparent affinity of hapten-reactive helper T cells during an immune response.

The maturation of helper T lymphocytes during an immune response was studied with respect to sequential changes in the functional specificity and affinity toward certain antigens. Protein-carrier (BαA)-reactive helper T cells obtained after a relatively long priming period were effectively stimulated by relatively lower doses of antigen than shortly primed helper T lymphocytes. When hapten (PAB)-reactive helper T lymphocytes were utilized as a model of helper T cells, reactivity also increased progressively to smaller concentrations of PAB-conjugates at successive intervals after primary immunization. Concomitantly, the cross-reactivity of PAB-reactive helper T cells to structurally related MAB- or OAB-determinants also decreased. Moreover, the PAB-reactive helper T cells of the relatively longer priming period were very susceptible to tolerance induction upon treatment with PAB-d-GL, whereas the reactivity of those helper T cells of the relatively shorter priming period was not abolished by this treatment. These results clearly indicate that there are qualitative changes in the helper T lymphocyte population during an immune response, and that this represents the sequential development or selection of helper T lymphocytes of higher specificity and apparent affinity to a corresponding antigenic determinant.     

Adoptive transfer of minor histocompatibility antigen-specific T lymphocytes eradicates leukemia cells without causing graft-versus-host disease.

Adoptive transfer of T cells reactive to minor histocompatibility antigens has the unmatched ability to eradicate malignant hematopoietic cells. Unfortunately, its use is hampered by the associated graft-versus-host disease. The critical issue of a possible dissociation of the antileukemic effect and graft-versus-host disease by targeting specific minor histocompatibility antigens remains unresolved because of the unknown nature and number of minor histocompatibility antigens necessary or sufficient to elicit anti-leukemic activity and graft-versus-host disease. We found that injection of T lymphocytes primed against a single major histocompatibility complex class I-restricted immunodominant minor histocompatibility antigen (B6dom1) caused no graft-versus-host disease but produced a curative anti-leukemic response. Avoidance of graft-versus-host disease required that no other host-reactive T cells be co-injected with T cells primed with B6dom1. Here we show that effective and non-toxic immunotherapy of hematologic malignancies can be achieved by targeting a single immunodominant minor histocompatibility antigen.     

Nature of the antigenic complex recognized by T lymphocytes. IV. Inhibition of antigen-specific T cell proliferation by antibodies to stimulator macrophage Ia antigens.

We have previously demonstrated that nonimmune guinea pig T lymphocytes could be specifically sensitized with TNP-modified allogeneic macrophages after eliminating the alloreactive T cells with bromodeoxyuridine (BUdR) and light treatment. This procedure allowed the unique opportunity to use anti-Ia sera directed against the Ia antigens of only the stimulator macrophages or responder T cells to determine against which cell type anti-Ia would block TNP-specific stimulation. It was found that the TNP-specific DNA synthetic response of BUdR and light-treated T cells stimulated with TNP-modified allogeneic macrophages was totally eliminated by anti-Ia sera directed solely against the allogeneic stimulator macrophage. In contrast, anti-Ia sera directed only against the responder T cells had no effect on their response to TNP-modified allogeneic macrophages. These findings indicate that macrophage Ia antigens are required for efficient T cell-macrophage interactions and raise the possibility that T cell Ia antigens may not be required for collaboration with macrophages. This latter possibility was substantiated by experiments in which we show that treating T cells with anti-Ia sera and complement to remove the Ia-positive cells either before or after priming, or both, had no effect on their ability to be primed and restimulated with TNP-modified macrophages.     

Formation of heterophile antibodies by human tonsilar lymphocytes: II. In vitro stimulation with allogeneic cells

Short-term cultures of human tonsilar lymphocytes (HTL), 5 × 10⁶ cells/culture, in medium RPMI 1640 supplemented with human group AB serum were studied for the production of plaque-forming cells (PFC) against sheep (SRBC) and bovine (BRBC) red blood cells following in vitro stimulation by various allogeneic lymphoid cells. Of 55 HTL specimens examined, 48 produced a significant number (50–300/culture) of PFC against SRBC and/or BRBC following the in vitro stimulation. The optimal doses of the stimulator HTL and peripheral blood lymphocytes (PBL) were 10⁷ and 5 × 10⁶/culture, respectively. After the stimulation, PFC appeared in significant numbers on the third day, reached the peak number on the sixth day, and decreased sharply in number thereafter. Removal of E-rosetting cells from both stimulator and responder populations abolished the PFC formation. PFC formation against SRBC was inhibited by solubilized Forssman antigen, while PFC formation against BRBC was inhibited strongly by Hanganutziu-Deicher antigen, hardly by Paul-Bunnell antigen and not at all by Forssman antigen. Supernatants of mixed lymphocyte culture of PBL were shown to enhance PFC formation of HTL cultures stimulated by allogeneic lymphocytes. The results of this study indicated that in vivo primed B cells of the HTL were triggered in vitro by allogeneic stimulation for the heterophile antibody formation. Since these antibodies are apparently directed against Forssman and Hanganutziu-Deicher antigens, the “allo” nature of these antigens as well as their relationship to the previously described heterophile transplantation antigens have to be clarified.     

Inhibition of normal mouse lymphocyte mitogen responses by xenogeneic or allogeneic antibodies to the MuLV glycoprotein gp71.

Xenogeneic and allogeneic antisera to the major envelope glycoprotein (gp71) of murine leukemia viruses (NyLV) inhibited the mitogenic response of normal mouse splenic lymphocytes to phytohemagglutinin (PHA) and lipopolysaccharide (LPS). This inhibition was specific for gp71 as demonstrated by the inability of xenogeneic antisera to other viral glycoproteins or structural proteins to inhibit and by the ability of purified antigens to block specifically the inhibitory effect. The ability of antisera to gp71 to inhibit LPS responses, however, is highly dependent on the strain and age of mouse spleen cells used and appears correlated with the expression of endogenous viruses. Moreover, the preferential inhibition of LPS responses suggests that this expression may be predominately B cell specific. The results suggest that the inhibitory effect is mediated via antibody binding to lymphocytes and that expression of viral envelope antigens on the cell surface which bind immunoglobulins can block or interfere with the binding or uptake of mitogens. A variety of natural mouse immune sera and "tumor" sera, having antibodies directed against gp71, can similarly inhibit mitogen responses; and this inhibition can be specifically blocked with MuLV or gp71.     

The lymphocyte restimulation system: Evaluation by intra-HLA-D group priming

Homozygous typing cells (HTC) were primed, using responding and stimulating lymphocytes of the same HLA-D groups. These intra-HLA-D group primings showed strong specific responses. Restimulation by HLA-D heterozygous and homozygous cell panels showed no correlation between the restimulating determinant and HLA-D. On the other hand, an unrelated individual, not carrying Dw4 and primed to Dw4 HTC, is restimulated by three of four Dw4-HTC. Thus, one non-HLA-D-associated restimulating determinant and another HLA-D-associated determinant could be identified. The differences among the four Dw4 HTC recognized in secondary MLC could reflect either recognition of separate gene products or recognition of separate determinants on the same gene product.     

Role of nominal antigen and Ia antigen in the binding of antigen-specific T lymphocytes to macrophages.

We have previously demonstrated that when primed T lymphocytes were repeatedly incubated on monolayers of antigen-pulsed macrophages (M phi), the cells that failed to adhere to the monolayer demonstrated a marked depletion of their proliferative response that was specific both for the antigen used for pulsing the M phi and for Ia determinants on the M phi. In order to further analyze the contribution of the nominal antigen and Ia antigens to the physical binding of T lymphocytes to M phi, we have attempted to block the absorption of T lymphocytes to M phi with a large excess of soluble antigen and with anti-Ia sera. Our results demonstrate that anti-Ia sera inhibit but that soluble antigen augments the binding of specific T lymphocytes to M phi. The implications of these findings for "dual recognition" and "linked recognition" models of T lymphocyte receptors are discussed.     

The immunoregulatory role of bone marrow. I. Suppression of the induction of antibody responses to T-dependent and T-independent antigens by cells in the bone marrow.

Bone marrow cells (BMC) from normal mice suppressed the in vitro IgM, but not the IgG, antibody (Ab) response of spleen cells. BMC were inhibitory only when added during the first 24 hr of culture, and inhibition was not due to an induced shift in the kinetics of the response. Addition of specifically activated T cells or nonspecific T-cell-replacing factors to normal or T-depleted spleen cell cultures did not abrogate suppression while the response to the T-independent antigen DNP-polymerized flagellin or lipopolysaccharide was also suppressed. BMC did not inhibit background Ab synthesis by normal or primed cells in the absence of antigen and did not inhibit, but stimulated, DNA synthesis in normal spleen cell cultures. In addition, high-avidity Ab synthesis was preferentially suppressed. A possible role for the bone marrow suppressor cell in the induction of B cell tolerance is discussed.     

Stimulator requirements for primed alloreactive T cells: macrophages and dendritic cells activate T cells across all genetic disparities

The cellular requirements for stimulating primed alloreactive T cells have been investigated. In vitro-primed secondary alloreactive cells, long-term lines, and Ly 1+2- noncytolytic clones which reacted with allo-H-2K, D, or Mls (M locus) antigens were tested. The data indicated that a specialized antigen-presenting cell such as a macrophage or a dendritic cell was required for stimulating primed alloreactive cells across all the genetic disparities tested. B and T lymphocytes were ineffective stimulators. The stimulator requirement for secondary and Ly 1+2- clone responses was heterogeneous, since both macrophages and dendritic cells were effective stimulators. Thus, the allostimulator requirement for inducing proliferation and mediator secretion by the primed T-cell populations closely paralleled the requirement for stimulating unprimed populations. The only exception found was the peritoneal washout population, which did not stimulate a primary response but did stimulate secondary responses. The failure of peritoneal macrophages to stimulate a primary response was shown to be due to an inhibitory pathway which did not occur when the responding population was alloantigen primed.     

Epstein-Barr virus (EBV) antigens processed and presented by B cells, B blasts, and macrophages trigger T-cell-mediated inhibition of EBV-induced B-cell transformation.

The ability of B cells, B blasts, and macrophages to present Epstein-Barr virion antigens to autologous T cells and trigger their capacity to inhibit Epstein-Barr virus-induced B-cell transformation was tested. Macrophages were as efficient as B cells and B blasts in presenting the virus to T lymphocytes. This function required antigen processing, because it was inhibited by chloroquine treatment and by fixation of the antigen-presenting cells immediately after viral exposure but not 18 h later. T cells exposed to the purified Epstein-Barr virus envelope antigen gp350 coupled to immunostimulating complexes also showed inhibitory function. These results suggest that recognition of processed virion antigens elicits the generation of T-cell-mediated inhibition of Epstein-Barr virus-induced B-cell transformation.     

Heterogeneity of HLA defined in PLT: a cellular assay detects differences not seen using HLA-DRw serology

The primed lymphocyte typing test (PLT) is used to detect the gene products of the HLA-D region which are responsible for secondary restimulation of cells primed in MLC. Alternatively, products of the HLA-D region may be detected serologically using antisera directed against a subpopulation of lymphocytes; these are the so-called DRw determinants. The PLT was used to see if it were possible to detect heterogeneity within a given serologically defined group using a cellular test. As priming combinations, we used family members identical for one haplotype and differing in the HLA-A, B and C regions, but not the D region of the second haplotype. Our results indicated that it was possible to prime against this second haplotype and that the segregation of the difference followed HLA. Therefore, using a cellular test it was possible to detect differences among cells belonging to a given DRw group. This suggests that PLT can be a useful tool to identify those serological groups which are composed of heterogenous determinants. In addition, it points out the problem in using any one test to establish identity of the HLA-D region, especially for clinical purposes.