Antigen-specific T-cell factor in cell cooperation. Mapping within the I region of the H-2 complex and ability to cooperate across allogeneic barriers

Clonotypic antibodies which stimulate T cell clone proliferation

We have prepared a variety of antisera which recognize the T cell receptors on both alloreactive and antigen-specific functional clones. The antisera specifically stimulate the immunizing T cell clones to proliferate without cross-stimulating a variety of other clones and are thus clonotypic. The antisera specifically precipitate an 82k molecular weight complex unique to the immunizing clone and an independent common component present on all the helper T cell clones tested. The 82k molecular weight complex consists of a heterodimer, which can be resolved into an acidic (a) chain and a more basic (beta) chain. The beta subunit differs in its isoelectric focusing pattern when isolated from two A derived clones which recognize and respond to different alloantigens. Thus, the functional specificity of the antibodies is reflected in identifiable changes in molecules at the biochemical level.

The mouse T cell receptor: comparison of MHC-restricted receptors on two T cell hybridomas

The receptors for antigen plus a major histocompatibility complex (MHC) gene product on a T cell hybridoma specific for ovalbumin plus a Class II MHC product were compared with those on another T cell hybridoma, specific for a Class I MHC product. In each case receptor material was identified by a clone-specific monoclonal antibody. The two receptors proved to have very similar gross structures, being 70-85 kd proteins, and reducing to an acidic alpha-chain and a slightly basic beta-chain, each 40-43 kd. The charge of both the acidic and basic polypeptides varied between the two receptors studied, showing that variable amino acid sequences occur in both chains.

Partial purification and characterization of an antigen-specific helper factor synthesized by a T-cell continuous line

Antigen-specific factors produced by the T-cell growth factor-dependent T-cell continuous line E-9M(+) were partially purified. Gel analysis of the twice-affinity-purified eluate of a poly(Tyr,Glu)-poly(DLAla)--poly(LLys) [(T,G)-A--L] column revealed the existence of iodinated bands with molecular weights of 17,000 and 15,000, in addition to a diffuse band of high molecular weight. The specific helper activity of the E-9M(+) supernatants was associated with a precipitate from 65-75% ammonium sulfate. Gel electrophoresis of either the eluate of a (T,G)-A--L column or of the 65-75% salt precipitate indicated that in both preparations two fractions contained the biological activity of the factor, one of a high (less than 67,000) molecular weight and the other of a low (15,000-17,000) one. Culture supernatants of the internally [35S]methionine-labeled E-9M(+) line were subjected to a combined purification of sequential ammonium sulfate precipitations, followed by affinity chromatography. Polyacrylamide gel patterns obtained of the eluates of the different salt precipitates demonstrated that the 65-75% ammonium sulfate precipitate contained two 35S-labeled bands with apparent molecular weights in the range of 60,000 and 15,000, similar to the activity patterns obtained by the gel electrophoresis fractionation experiments. Thus, it is suggested that a fraction of low molecular weight preserves the antigen specificity and the helper activity of the factor produced by the T-cell line.

Genetically regulated human (T,G)-A-L specific helper T cell replacing factors possess HLA-DR and VH determinants

Human (T,G)-A-L specific T cell helper factors secreted by in vitro activated peripheral blood lymphocytes of normal donors were characterized. Factors were passed through columns of Sepharose coupled either to antibodies against human immunoglobulin or antibodies against the variable region of the heavy (VH) and light (VL) chains of human immunoglobulin. In addition, the same factors were applied to columns of Sepharose coupled to anti-HLA-DR antibodies or to monoclonal antibodies against human Ia or beta 2-microglobulin. The activity of the antigen specific factors was removed by the anti-VH antibodies and not by anti-VL or anti-human immunoglobulin antibodies. The factors passed through Sepharose coupled to anti-DR antibodies could be removed and eluted from columns of anti-DR antibodies relevant to the donors' DR antigens. The same factors were also removed by a monoclonal antibody (anti-Ia) which recognizes a monomorphic determinant on HLA-DR, but not by monoclonal anti-beta 2-microglobulin. The results suggest that the genetically regulated (T,G)-A-L specific helper factors possess HLA-DR as well as VH determinants in their active moiety.

The major histocompatibility complex-restricted antigen receptor on T cells. I. Isolation with a monoclonal antibody

An antibody-secreting B cell hybridoma, KJ1-26.1, has been prepared from mice immunized with the T cell hybridoma DO-11.10, which recognizes chicken ovalbumin in association with I-Ad (cOVA/I-Ad). KJ1-26.1 blocks I-restricted antigen recognition by DO-11.10 and a subclone of this T cell hybridoma, DO-11.10.24, which has the same specificity for cOVA/I-Ad as its parent. KJ1-26.1 does not block I-restricted antigen recognition by any other T cell hybridoma tested, including a number of T cell hybridomas closely related to DO-11.10, with similar, but not identical, specificities for antigen/I. Moreover, KJ1-26.1 binds to DO-11.10 and DO-11.10.24, but not to any other T cell hybridomas tested, including three subclones of DO-11.10 that have lost the ability to recognize cOVA/I-Ad. Thus, in every regard KJ1-26.1 appears to be binding to all or part of the receptors for antigen/I on the T cell hybridoma DO-11.10. KJ1-26.1 appears to bind to approximately 15,000 molecules/cell on the surface of DO-11.10. The antibody precipitates an 80,000 dimer from the cells, which on reduction migrates as 40-44,000 monomers. The receptor(s) for antigen/I on DO-11.10 therefore includes molecules with these properties.

Characterization of T-cell-soluble factors modulating the expression of Ia and H-2 antigens on BALB/c B lymphoma cell lines

The effect of supernatants of concanavalin A-activated spleen cells (CAS) on the expression of various antigens, especially Ia antigens, on BALB/c B lymphoid cells, was examined. This study demonstrates the following: (i) CAS enhanced the expression of Ia antigens on four out of five BALB/c lymphoid cell lines. (ii) CAS selectively modulates the expression of Ia and H-2D, but not sIgM or viral gp70 expression, on X16C 8.5 tumor cells. The enhanced levels of Ia expression on B lymphoid tumor cells were also detected by using anti-Ia monoclonal antibodies. (iii) The molecular weight of soluble factor(s) affecting Ia and H-2 was approximately 40,000 estimated by gel filtration on a Sephadex G-200 column. (iv) Type 1 interferon but not interleukin 1, interleukin 2, or T-cell-replacing factor enhanced the expressions of Ia and H-2D antigens. (v) The activity of CAS-modulating Ia and H-2 antigens was eliminated by acidic treatment. It was concluded from this study that at least one of the factor(s) in CAS, modulating the antigenic expression of B-lymphoid cells, was interferon-like in nature. From our findings, a possible immunoregulatory mechanism by interferon was suggested: T cells, after stimulation of mitogens or antigens, secrete interferons which modulate the expression of Ia and H-2 on B cells. Then B cells, whose Ia and H-2 were modulated selectively by T-soluble factors(s), might interact with T cells much more efficiently.

Use of somatic cell genetics to study chromosomes contributing to antigen plus I recognition by T cell hybridomas

Keyhole limpet hemocyanin (KLH)/I region-specific T cell hybridomas have been prepared by fusing KLH/I-specific T cell blasts from mice with single pairs of metacentric chromosomes to the inducible, interleukin 2 (IL-2)-secreting T cell hybridoma FS6-14.13.AG2.1. T cell hybridomas with KLH/I receptors were identified by their ability to secrete IL-2 in response to KLH and the appropriate antigen-presenting cells. After cloning and subcloning, KLH/I reactivity was correlated with the presence or absence of metacentric chromosomes derived from the KLH/I-specific T cell blast parent. Hybridomas were identified that had lost all chromosomes 4 and 6 or 16 and 17 derived from their normal T cell parent, but retained the ability to respond to KLH/I. This suggested that products of genes on these chromosomes did not contribute to the specific portions of T cell Ag/I receptors. These gene products would include, of course, kappa and lambda chains and H-2. We did not obtain any T cell hybridomas that had lost both metacentric (8.12) chromosomes derived from T cells of the Robertsonian mouse strain Rb(8.12)5, so we could not draw any conclusions about the contributions of products of genes on these chromosomes. T cell hybridomas with KLH/I reactivity were found that contained only one metacentric (8.12) chromosome derived from this strain. Moreover, a T cell hybridoma was found that retained both metacentric (8.12) chromosomes from its normal T cell parent, but had lost KLH/I reactivity. These results suggested that neither two chromosomes 8 nor two chromosomes 12 were required for antigen/I reactivity in normal T cells and that antigen/I reactivity was controlled, at least in part, by genes mapping on chromosomes other than 8 or 12.

Non-H-2 restriction of expression of passively transferred delayed sensitivity

The results of this study of allogeneic restriction of passively transferred delayed sensitivity to Listeria antigens serve to illustrate the complexity of in vivo models. They show that the H-2 restriction observed when delayed-type hypersensitivity was transferred between H-2-congenic strains was no more severe than the restriction observed when delayed-type hypersensitivity was transferred between parental and F1 mice and between different strains sharing the same H-2 haplotype. It is obvious that genes, in addition to those of the H-2 locus, can be responsible for allogeneic restriction in vivo.

Regulatory factors of lymphocyte-lymphocyte interaction. II. Characterization of human mitogenic factor derived from the culture supernatant of a mouse-human hybridoma

Cell hybridization of phytohemagglutinin (PHA)-stimulated human peripheral blood lymphocyte (PBL) with murine lymphoma (EL-4) provided three hybridomas (MHH-16, MHH-20, and MHH-22) which spontaneously produced human mitogenic factor (MF). MHH-16 was serially subcloned by limiting dilution procedures, which resulted in maintaining two subclones producing human MF spontaneously for more than one year (PQL-3 and PQL-5 subcloned lines). Human MF MHH-MF) derived from supernatants of PQL-5 line cultures had a molecular weight (m.w.) of about 26,000-30,000 daltons (the major peak) with a minor peak with an m.w. of 15,000 daltons on Sephadex G-100 chromatography, and at a high concentration of NaCl (1 M), the activity of the 26,000-30,000-m.w. fraction became weak and that of the 15,000-m.w. fraction became predominant. MHH-MF had an isoelectric point of Ph 5.0-6.5. On DEAE-cellulose chromatography, MHH-MF was eluted at a fairly low salt concentration (sodium phosphate buffer 0.02 M, pH 8.0, NaCl 10 mM). After periodate treatment of this MHH-MF, the mitogenic activity almost disappeared. MHH-MF was relatively unstable to heating at 56 c for 20 min. In the presence of tunicamycin (0.3 microgram/ml), an inhibitor of N-linked glycosylation the synthesized MHH-MF showed a decrease in m.w. as follows: the major peak shifted from 26,000-30,000 to 23,000 daltons and the minor peak from 15,000 to 10,000 daltons on Sephadex G-100 chromatography. In internal labeling experiments with [3H] leucine, the 3H-labeled MF was partially purified, with mitogenic activity as a guide. This 3H-labeled MHH-MF fraction could be absorbed by PHA blasts but not by normal PBL. On SDS-PAGE under reducing conditions, only the radioactive peak of the 15,000-dalton fraction was recovered. MHH-MF obtained from the hybridoma culture supernatants may be a dimer of the 15,000-dalton fraction and a glycoprotein.

Analysis of unexpected inhibitions of T lymphocyte proliferation to soluble antigen, alloantigen and mitogen by unfragmented anti-I-Ak or anti-I-E/Ck monoclonal antibodies

We investigated the capacity of anti-I-Ak and anti-I-E/Ck monoclonal antibodies (m.Ab.) to inhibit T lymphocyte proliferative responses to soluble antigen (Keyhole limpet hemocyanin), alloantigens (H-2 or non-H-2 related) and a mitogen (Concanavalin A). Surprisingly, specific inhibition was observed in all circumstances, and with both anti-I-Ak and anti-I-E/Ck m.Ab., whether the responses tested were I restricted in cell mixing experiments or not. The significance of the inhibition by anti-Ia m.Ab. of non-Ia-restricted responses is still not completely understood. These results, however, strongly suggest that in vitro inhibition by anti-Ia antibodies of T cell proliferative responses does not necessarily indicate I restriction of the presentation to T lymphocytes of the corresponding antigen.

Triggering of affinity-enriched B cells. Analysis of B cell stimulation by antigen-specific helper factor or lipopolysaccharide. I. Dissection into proliferative and differentiative signals

Proliferative and differentiative signals controlling the in vitro IgM response by unprimed, affinity-enriched B cells were studied using conditions under which as few as 2,000 B cells stimulated by antigen-specific, Ia-positive, allogeneically restricted, T cell-derived helper factor (Hf) or the polyclonal activator lipopolysaccharide (LPS) yielded on the average 400 antibody-forming cells (AFC) by direct plaque assay. Antigen alone induces neither B cell proliferation nor differentiation into AFC. Proliferation but not differentiation into AFC is induced when affinity-enriched B cells are cultured in the presence of Ag and Hf or LPS but in the absence of nonantigen-specific, radioresistant, accessory (A) cells. For the induction of a complete Hf- or LPS-mediated AFC response, cultures must be reconstituted with A cells or the secretory product(s) of these cells. The antigen-specific response depends strictly on the presence of the Hf specific for the relevant antigen, regardless of the cell cycle state of cooperating B cells. The differentiative signal from A cells is due, at least in part, to the presence of a Thy-1.2-bearing population of cells. In the case of the LPS-mediated, but not the Hf-mediated response. A cells can be substituted by using supernatant derived from an interleukin 2-secreting T lymphoma cell line (EL4). In the presence of histocompatible Hf and B cells, histoincompatible A cells can still cooperate in the immune response. However, the degree of allogeneic restriction between incompatible Hf and B cells is markedly increased if both B cells and A cells are incompatible with Hf.

The role of regulatory components from resident T lymphocytes in polyclonal B cell activation

Resident T lymphocytes have been found to exert helper and suppressor regulatory influences with regard to polyclonal activation of murine splenic B lymphocytes elicited by lipopolysaccharide. In the normal adult spleen, only T cell helper influences are exercised over polyclonal B cell activation. This activity is a property of Lyt 1+2- T cells and does not appear to be subject to MHC restriction. Suppressive influence evidently is either latent or it exists at such a low level that its effects are difficult to detect. No regulatory activity can be recovered from the supernatants of T cells, cultured either with or without LPS. However, suppressor T cell function may be evoked by activating splenic T cells with Concanavalin A or by sonicating unstimulated splenic T cells in order to liberate a suppressive potential which is not expressed by these unstimulated cells when intact. The soluble fraction of resident splenic T cell sonicates exerts both helper and suppressor regulatory influences. The soluble helper activity is derived from Lyt l+2- T cells, whereas suppressor activity is generated from Lyt 1-2+ T cells. The suppressive activity of T cell sonicates is not restricted by the MHC gene complex. Helper and suppressor activities contained in splenic T cell sonicates were separated by gel chromatography; the suppressive activity was found to elute with a molecular weight between 68,000 and 84,000 daltons, and the helper activity eluted with a molecular weight between 15,000 and 23,000 daltons. The data indicate that helper and suppressor activities are distinct molecular entities derived from distinct splenic T lymphocyte subpopulations. The possibility that these molecules are precursors to or components of antigen-specific or nonspecific helper and suppressor factors described in the literature is discussed.

H-2-restricted helper factor secreted by clone hybridoma cells

Biological and serological characteristics of a helper factor secreted by cloned hybridoma cells was described. The factor is carrier specific and contains determinants shared with immunoglobulin VH bu does not react with V kappa- or V lambda-specific antibodies. Presence of four H-2I-controlled antigenic specificities, Ia.ml, Ia.m2, Ia.17, and Ia.m7, was detected. Hence, it is possible that both A beta and E alpha loci may be involved in its control. Helper effect could be obtained only toward B cell sources that shared the H-2K and I-A antigens with the hybridoma cells. Similarly, the factor was absorbed only by spleen cells syngeneic in I-A. Previous studies have demonstrated that this clone binds antigen in an H-2-restricted manner. It follows that H-2-restricted helper cells produce H-2-restricted helper factors. Hence, they support the view that specific T cell factors may represent secreted T cell receptors.

Immune response potential to poly(Tyr,Glu)-poly(DLAla)--poly(Lys) of human T cells of different donors

Human peripheral blood T cells of normal donors were activated in vitro with autologous adherent cells pulsed with poly(LTyr,LGlu)-poly(DLAla)--poly(LLys) [abbreviated (T,G)-A--L]. The "educated" T cells were tested: (i) for their ability to produce a (T,G)-A--L-specific T cell-replacing factor in the cooperation with B cells for antibody responses in vivo or in vitro and (ii) for their ability to proliferate in the presence of a second stimulus of (T,G)-A--L. Results of screening of 66 donors demonstrated that educated T cells of about 50% of the donors produced an active (T,G)-A--L-specific factor, whereas activated cells of only half of the factor producers were capable of proliferating in the presence of the antigen. Thus, as reported for all other species studied, human individuals differ in their response potential to (T,G)-A--L.

Presence of interchain disulfide bonds between two gene products that compose the secreted form of an antigen-specific suppressor factor

The secreted form of the suppressor T cell factor specific for keyhole limpet hemocyanin derived from the hybridoma 34S-704 was found to consist of the two distinct polypeptide chains, i.e., the antigen-binding and the I-J-encoded chains. They were linked in covalent association with disulfide bonds. The two chains were cleaved by the reduction with dithiothreitol and were easy to reconstitute the active form of TsF. The association of the two distinct chains was suggested to be essential for the expression of the TsF activity.

Regulation of the human allogeneic proliferative response in vitro

We have investigated the glass-wool-adherent characteristics of human lymphocytes able to suppress allogeneic proliferation in vitro. We observed that: (1) Suppressor cells obtained after in vitro priming and their precursors are adherent to glass wool, whereas cytotoxic cells and their precursors are not; (2) primed cells adherent to glass wool are mainly HLA-DR positive, while nonadherent cells are HLA-DR negative or weakly positive; (3) the nonadherent, unprimed T cells used as responder cells in a primary MLR are more readily suppressed by suppressor cells than the same cells unfiltered. This may suggest an enrichment of 'acceptor' cells for suppression.

Intra-H-2 recombination in the mouse. III. I-Region characterization of haplotypes H-2at2, H-2at3 and H-2a2

Serological characterization of three K-S interval recombinant strains, TBR2 (H-2at2), TBR3 (H-2at3) and AIR 1 (H-2a2) was performed using anti-H-2, Ia, Ss and Slp antisera. The data presented here reveal that the crossover events in both TBR2 and TBR3 occurred between the I-A and I-E subregions. In both cases, the H-2K and I-A subregions were derived fron the H-2t1 of chromosome, while the I-E, S and H-2D regions were derived from the H-2b chromosome (KsAkEbSbDb). The H-2a2 chromosome resulted from a crossover event between the H-2a1 and H-2i9 chromosomes. Ia and Ss typing of AIR 1 suggested that the K to I-E regions originated from H-2a1 and the S and D regions originated from H-2i9 (KkAkEkSbDd).

Biochemical comparison of HLA-DR molecules derived from autologous human T and B lymphoblasts

Earlier findings that human activated T blasts display HLA-DR determinants have been confirmed. After phytohemagglutinin activation, Percoll gradient-purified blast cells were cultured for two weeks in mitogen-derived supernatants from human lymphocyte cultures. Using purified T blasts and internal labeling procedures, it was established that T blasts actively produced HLA-DR-like chains, as assessed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Further, HLA-DR chains obtained from Epstein-Barr virus-transformed B cells and from T blasts of the same donor were compared. Two-dimensional gel electrophoretic comparisons indicated a striking homology between 29 kD and 35kD chains, obtained from the two different cell types. Peptide map analysis and preliminary amino acid sequence comparisons further supported this similarity. A more complete analysis would, however, be required to prove actual identity. The fact that human T blasts produce and display HLA-DR molecules very similar, if not identical, to those present on B cells must then be incorporated into models discussing major histocompatibility complex-restricted collaborations involving HLA-DR molecules.

Antigen-specific T-cell factors

Antigen-specific T-cell factors are mediator molecules which are produced by helper and suppressor T cells and which can perform the function of those cells in an antigen-specific manner. They probably play an important part in immunoregulation. The major histocompatibility complex has a controlling influence on their structure and activity, while their antigen-recognition properties may be conferred by immunoglobulin V regions. Interest in the factors derives from three related areas of research, namely (i) the problem of T-cell recognition of antigen; (ii) the mechanisms of cellular interactions in antibody production and cell-mediated immunity; and (iii) the genetic control of immune responses. This review discusses the literature up to June 1980 on their production, structure, genetic restriction and mechanism of action.

Production and main characteristics of a fetal calf serum-specific cell line that induces T and B cell differentiation

Spleen cells from B6 mice injected with fetal calf serum (FCS) could be kept proliferating as a continuous cell line in vitro provided they were culture in the presence of irradiated syngeneic spleen cells and FCS. Cells in this cell line showed a strong proliferative response when stimulated with concanavalin A (Con A), and they were able to mediate the following functions: (1)they helped the generation of alloantigen-specific cytotoxic T lymphocytes (CTL) from thymocyte-spleen cell mixed lymphocyte cultures (MLC), (2)they induced the generation of CTL from normal syngeneic spleen cells in the absence of allogeneic stimulator cells, and (3)they induced normal spleen cells to differentiate into anti-sheep erythrocyte (SRBC) plaque-forming cells (PFC), in the absence of SRBC in the cultures. The use of this cell line (called line 12) may thus provide an interesting approach for the study of cellular and molecular requirements for cell-cell interactions and for the differentiation of T and B effector functions.

Concanavalin A-inducible, interleukin-2-producing T cell hybridoma

The fusion of an AKR T cell tumor line to normal B6D2F1, T cells resulted in the production of a cloned T cell hybridoma (FS6-14.13) inducible with the mitogen concanavalin A (Con A). The supernate from Con A-stimulated hybridoma cells was active both in the stimulation of an anti-sheep red blood cell response by partially T cell-depleted B cells and in the stimulation of the growth of antigen-specific T cell blasts. The active principle in both assays had a molecular weight of approximately 30-40,000. These results indicated the presence of interleukin 2 (IL2) in the hybridoma supernate. The activity of the hybridoma supernate in B cell responses was dependent on the presence of adherent cells and a few contaminating T cells. On the other hand, Con A-stimulated supernates from normal spleen cells were active after either adherent cell removal or severe T cell depletion. These results suggested that IL2 was the only active helper factor in the hybridoma supernate, but that additional helper factors were present in supernates from Con A-stimulated normal spleen cells.

T-cell hybridoma bearing heavy chain variable region determinants producing (T,G)-A--L-specific helper factor

Thymus-derived lymphocytes (T cells) exert their regulatory effect (help or suppression) on the antibody production by B cells either by direct cell to cell interaction or by soluble mediators or factors. The low frequency of specific T cells, the heterogeneity of their responses and their relatively short life span have hampered the molecular characterization of the antigen recognition unit of T cells, and its structure is largely unknown. The lymphocyte hybridization technique, which has been found very useful for the production of B-cell hybridomas secreting specific monoclonal antibodies, has also been used for the generation of homogeneous and stable T-cell hybridomas with unlimited growth potential. So far the only specific effector function demonstrated in the established T hybridomas is the property to generate a factor(s) which suppresses antibody responses. We now describe the establishment of hybrid lines which exhibit characteristic T-cell markers. One of the hybridomas (denoted R-9) releases into the culture supernatant factor(s) with helper activity specific to the synthetic polypeptide (T,G)-A--L and bears surface determinants of the immunoglobulin heavy chain variable region (VH). Such hybrid cell lines are of great value for studies on the nature of the T-cell receptor.

Round cells of the epidermis: clues from studies on neoplastic lymphocytes of cutaneous T cell lymphoma

Neoplastic cells of cutaneous T cell lymphoma (CTCL) appear to be of monoclonal origin and frequently are nonspecific helpers of normal B cell differentiation. A natural progression from epidermotropic (mycosis fungoides and Sézary syndrome) to nonepidermotropic, more widely disseminated T cell neoplasms generally occurs. Affinity of CTLC cells for the epidermis may result from their having membrane receptors for histocompatibility (Ia) antigens present in skin. Cultured human epidermal cells produce a thymopoietin-like molecule, an indication of a role for skin in T cell differentiation.

Antigen specific T cell factors

Antigen specific helper and suppressor factors have a similar structure, with two major sections, a 'variable region', determining antigen specificity which is likely to be controlled by Immunoglobulin VH genes, with which it shares idiotype and framework determinants. Specific factors also have a 'constant region' which does not vary between strains and minimally between species or with the antigenic specificity of the factors, which are defined by rabbit anti-helper or anti-suppressor antisera. This region determines the biological function of the molecule. Anti-Ia antisera react with factors, but the nature and function of Ia molecules on T cell factors is still unclear. The model of specific factor structure, with C and V regions resembles that of immunoglobulin, and it is thus possible that the C region of factors, like the V region is Ig linked. Because there are multiple T cells, helping and suppressing antibody responses specifically, it seems improbable that all of these cells could interact directly with rare antigen-specific B cells. Thus we propose that macrophage presenting cells are the key to the integration of signals for immune induction and regulation for T and B cells. Since Ir genes have been identified in the macrophage presenting cells interacting with both T and B cells, this suggests that macrophage Ia antigens are of importance in the integration of triggering signals for the lymphoid pool.

Functional and molecular organisation of an antigen-specific suppressor factor from a T-cell hybridoma

Thymus-dependent (T) lymphocytes have been shown to have antigen specificity. The antigen receptor on T lymphocytes, in contrast to that on B lymphocytes, does not appear to be of the conventional immunoglobulin (Ig) type. Studies on the antigen-specific factors derived from helper and suppressor T cells (Ts) demonstrated that they possess determinants with antigen binding affinity and products of genes in the H-2 complex (MHC). Furthermore, antibodies against the variable region of Ig heavy chains or idiotypes have been shown to react with T-cell antigen receptors as well as antigen-specific helper and suppressor T-cell factors (TsF). It is, therefore, conceivable that at least two gene products are involved in the structural entity of these receptors: one each coded for by genes in either. To establish the molecular nature of the recognition component of T cells we have used homogeneous TsF from a T-cell hybridoma with a specific function. We report here that the antigen binding and I-J coded molecules on TsF are independently synthesised in the cytoplasm, and are secreted as an associated form of the two molecules; this association is required for antigen-specific suppression of antibody response.

Role of self carriers in the immune response and tolerance. V. Reversal of trinitrophenyl-modified self suppression of the B-cell response by blocking of H-2 antigens

Trinitrophenylated syngeneic spleen cells (TNP-SC) are potent tolerogens of the anti-TNP plaque-forming cell (PFC) response in vivo and in vitro. This unresponsive state requires T cells for both its induction and maintenance. Because H-2K/D-restricted cytotoxic T cells are also induced by exposure to TNP-SC, we determined the role(s) of histocompatibility antigens (K, I, and D) in the suppression of the PFC response by TNP-SC. We treated syngeneic TNP-modified stimulator cells with antiserum directed at K-, I-, or D-region determinants and found that blocking of H-2K or D antigens on TNP-SC transformed these tolerogens into immunogens capable of eliciting an anti-TNP PFC response in the absence of extrinsic immunogens like TNP-polymerized flagellin. In H-2k or H-2a(k/d) mice, only H-2Kk needs to be blocked on the stimulator cells, whereas H-2K or D recognition was apparent in B10.A(4R) mice. These observations indicate that suppression of the PFC response by TNP-SC shows the same restriction in recognition as does the cytotoxic T-cell response. Furthermore, our results suggest that TNP-I-A is recognized by the helper cells in this system as the intrinsic antigen. When both TNP-K and TNP-I-A are present and available on the same stimulator cell, suppression (via modified K recognition) is dominant over help.

Comparison of antigen-specific I-region-associated cell interaction factors

Two basic types of factors reacting with anti-I region (anti-Ia) antisera are compared, those derived from macrophage-like antigen presenting cells and others derived from T-lymphocytes, of either the suppressor or helper type. Despite the common property of reacting with anti-Ia antisera, the two sets of factors differ by many criteria. Macrophages, upon culture with antigen, release complexes of Ia antigen and a fragment of the original immunogen. This material is only produced by responder macrophages and thus appears to be a soluble Ir gene product. The genetic restriction of the T-macrophage interaction was investigated in chimeras, and it was found that the host environment as well as the donor genotype was of importance in determining restrictions, which were thus not really directed to "self." There was no evidence for intrinsic T-cell Ir genes, as nonresponder stem cells developed into responder T-cells in a (responder X nonresponder) F1 environment. However, these cells only responded in the presence of responder macrophages. Specific T-cell factors are different in nature. These all react with anti-Ia antisera, but the nature or function of the T-cell Ia is unknown. The basic structure involves a VARIAble region" responsible for antigen binding which, as it reacts with anti-idiotype antisera and anti-variable region framework antisera is an immunoglobulin variable region. There is also a "constant region," defined by its biological properties as well as by specific rabbit antisera. This two-region nature of specific factors is reminiscent of immunoglobulin structure and it is a reasonable hypothesis that the constant region is linked to the Ig cluster of genes.

Regulatory mechanisms in cell-mediated immune responses. VIII. Differential expression of I-region determinants by suppressor cells and their targets in suppression of mixed leukocyte reactions

The phenotypic expression of I-region determinants on cells producing and responding to MLR suppressor factor (MLR-TsF) was established in these studies. Alloantigen-activated MLR suppressor T cells (MLR-Ts), which produce MLR-TsF bearing gene products of the I-C subregion, were exposed to anti-I subregion sera and complement (C) before in vitro culture for MLR-TsF production. Suppressor activity was prevented by removal of cells bearing I-C determinants, whereas elimination of cells expressing I-A/B determinants had no effect. Interestingly, cytotoxic elimination of cells displaying I-J determinants also prevented MLR-TsF production. Admixture of anti-I-J and I-C antiserum-treated cells for MLR-TsF production failed to reconstitute suppressor activity, indicating that I-C and I-J gene products are expressed on a single population of cells critical to MLR suppression, rather than on distinct interacting subpopulations. Anti-I-C serum activity specific for I-C+ MLR-Ts was removed by adsorption with nylon wool-nonadherent splenic T cells and concanavalin A-activated thymocytes; adsorption with splenic B cells from anti-Thy-1,2 serum and C-treated spleen failed to remove relevant anti-I-C activity. These data suggest that regulatory I-C molecules, like I-J molecules, are preferentially expressed on T lymphocytes. Expression of I-C, or other I-region molecules on responder cell targets of MLR-TsF activity was also investigated. Responder cells were pretreated with anti-I subregion-specific sera in blocking or complement-dependent cytotoxic protocols before addition to MLR with MLR-TsF. Neither blocking nor the cytotoxic removal of cells bearing I-C or other I-region determinants from MLR responder populations interfered with MLR-TsF suppression. Because it has previously been demonstrated that MLR-TsF interacts optimally with activated, I-C syngeneic target cells, blocking and cytotoxic studies with anti-I subregion sera were also performed with responder cells activated by 24 h culture in MLR in the absence of MLR-TsF. Brief MLR-TsF pulse after antiserum treatment generated marked suppression regardless of blocking or absence of cells bearing serologically detected I-region determinants. I-C restricted suppression may thus be mediated not by interaction with I-C-bearing cells, but by target cells which exist in requisite association with populations of I-C+ cells.

Selective production of human antigen specific helper factor from normal volunteers: implications for human Ir genes

Based on previous systems for generating helper cells and factors from mouse spleen cell cultures, an in vitro system for the production and detection of human helper factors to the synthetic polypeptide antigens (T,G)-A--L and GAT10 was developed. The factors are made by human peripheral blood leucocytes and are antigen-specific, as judged both by functional criteria and specific binding and elution from antigen columns. Out of the first six volunteers studied two were high responders to (T,G)-A--L, but non-responders to GAT, two responders to GAT but not (T,G)-A--L. One subject made factors to both antigens and the sixth reacted to neither. The antigens chosen are known to be under MHC-linked immune response (Ir) gene control in all animal species tested, with some strains being responders while others are not. The selective responsiveness, different between individuals, thus suggests that the response to these antigens in man is under Ir gene control. Because of the small size of the sample initially studied and HLA typed, it was not surprising that there was no clear-cut association of response with any particular histocompatibility type at the HLA-A, B, C or D locus.