Properties of reticulum cell sarcomas in SJL/J mice. VIII. Prominent role of RCS cell I-A antigens in the stimulation of syngeneic T cells

Functional significance of polymorphism among MHC class II gene promoters

The functional significance of polymorphism among MHC class II promoters in man and mouse is here reviewed, mainly in terms of the hypothesis of differential expression. The hypothesis proposes that differences between antigen-presenting cells in MHC class II expression exert a co-dominant effect on the Th1-Th2 cytokine balance, such that class II molecules of one type come to control to a greater extent the production of one group of cytokines, and those of another type the production of the alternative group. The survey deals with the influence of signal strength and antigen-presenting cell type on T-cell subset differentiation; functional differences between MHC class II molecules not obviously related to determinant selection; disease protection mediated by HLA alleles; mechanisms possibly responsible for allotypic and isotypic bias; overdominance (heterozygous advantage) in selection for expression of class II alleles; MHC class II promoter structure and function; inter-locus and inter-allele variability within human MHC class II gene upstream regulatory regions; a comparison of these polymorphisms in mouse and man; read-out of class II promoter function; and a comparison with expression of MHC class I. We conclude that the evidence that this variation is functionally active (i.e. controls expression) is increasing, but is not yet compelling. The crucial test still to come, we suggest, is whether or not the biological effects attributable to this polymorphism will line up with molecular studies on expression.

IL-10 production in a CD5+ B cell lymphoma arising in a CD4 monoclonal antibody-treated SJL mouse

A majority of SJL mice develop spontaneous reticulum cell sarcomas (RCS) at about 1 year of age which can be transplanted into young SJL recipients. Previous studies have shown that RCS tumors are of B cell lineage, and that the development of these lymphomas and their subsequent growth depends upon host-derived T helper cell factors. In vivo treatment of SJL mice with anti-CD4 monoclonal antibody (mAb) prevents the development of the characteristic B lymphomas. Most of the mAb-treated animals were tumor free and had a significantly prolonged life span. However, one such CD4 mAb-treated mouse developed a transplantable IgM+ CD5+ B cell lymphoma (designated NJ101), which has not previously been described in SJL/J mice. NJ101 is clonal on the basis of a discrete non-germ line Ig heavy chain gene rearrangement by Southern blot analysis. Unlike the sIg- CD5- transplantable RCS-X cell line, the IgM+ CD5+ NJ101 lymphoma cells will grow in immuno-compromised hosts, such as irradiated recipients or in recipients treated with CD4 mAb in vivo. The RCS (B cell) lymphoma requires CD4+ T cells for progressive growth, whereas the growth of the CD5+ B lymphoma cells is enhanced by the removal of such cells. Thus, CD5+ B cell clonal development may be aided by the removal of regulatory T cells and/or the malignant CD5+ B cells may produce their own growth factors in an autocrine manner. Examination of IL-10 message by quantitative polymerase chain reaction techniques indicate that the CD5+ B lymphoma cells produce increased levels of IL-10 relative to normal LN cells or purified RCS lymphoma cells. These results suggest that two different types of B cell tumors, both of which can develop in SJL mice, have different growth requirements. Furthermore, treatment to prevent the occurrence of the characteristic RCS malignancy of SJL mice may lead to the development of another form of B cell neoplasia.

I-E expression does not by itself influence growth of or T cell unresponsiveness to SJL lymphomas

The nature of the antigen on SJL lymphoma (reticulum cell sarcomas, RCS) cells that is strongly stimulatory to syngeneic CD4+ T cells is still elusive. Previously, we showed that the response to RCS of T cells from F1 hybrids of SJL by strains expressing I-Ak,d and/or I-Ek,d was much lower than that of T cells from SJL mice or from F1 hybrids of SJL by H2b- or H2s-bearing strains. We now show that removal of CD8+T cells from the responding cell population of (SJL x BALB/c)F1 or (SJL x A.TL)F1 mice does not enhance their responses, suggesting that the negative effect of H2k,d is not due to suppressor cells. Moreover, repeated injections of RCS cells into such F1 mice also fail to enhance the response, suggesting that these mice lack responder cells. T cells from I-E alpha transgenic (C57BL x SJL)F1 mice backcrossed to SJL respond to RCS as do T cells from I-E alpha- littermates or SJL mice. Similarly, I-E alpha+ SJL mice support RCS growth in vivo to the same (LN + spleen)/body weight ratio as do I-E- littermates. Thus, while I-E appears to have a negative influence on T cell responsiveness and RCS growth in F1 mice, it does not have such an effect when present, by itself, on a SJL background. The role of V beta 17 a+ T cells in the response of SJL T cells to RCS was also examined, because such cells are known to be responsive to I-E. The responses of V beta 17a(+)-depleted (0.3% V beta 17 a+) and V beta 17 a(+)-enriched (25.3% V beta 17a+) SJL T cell populations to RCS were examined by limiting dilution. We found the incidence of responding cells to be slightly higher in the depleted (0.016%) than in the (0.006%) enriched population. Furthermore, lymph node blast cell populations responding to RCS do not exhibit a higher percentage of cells staining for V beta 17a than do blast cells responding to Con A or unstimulated lymph node cells.

Reticulum cell sarcomas of SJL mice have rearranged immunoglobulin heavy and light chain genes

The immunoglobulin (Ig) heavy (H) and light (L) chain gene rearrangements of the high incidence SJL lymphomas (reticulum cell sarcoma, RCS) have been analyzed. Both primary and transplanted RCS show rearrangements of H and kappa L chains, demonstrating that these tumors are of B cell origin. These data are consistent with previous results indicating that these tumors are a mouse model for follicular lymphoma. A long-term transplanted line and the in vitro line derived from it, cRCS-X, have a single rearranged JH-C gamma 2a fragment and one rearranged C alpha gene fragment which does not hybridize with a probe for the JH gene segments. These cell lines also have two rearranged J kappa-C kappa fragments. Primary tumors and early passages are more heterogeneous with respect to Ig gene rearrangements, possibly because more than one B cell clone is present. Although no synthesis of IgG2a, or of any Ig, could be detected by the in vitro cRCS-X cells, these cells contain abundant poly(A)+ RNA that hybridize with gamma 2a and kappa probes as well as lesser amounts of alpha and epsilon RNA. None of these H chain RNA hybridized with probes for the JH gene segments. The epsilon and alpha RNA are the same size as transcripts of germ-line CH genes which have been identified in other systems. However, the gamma 2a RNA are smaller than previously described germ-line C gamma 2a RNA and appear to be transcribed from aberrantly rearranged JH-C gamma 2a genes.

T-helper-cell-specific monoclonal antibody inhibits growth of B-cell lymphomas in syngeneic SJL/J mice

Transplantable follicular center cell lymphomas of SJL/J mice are B-cell tumors that stimulate proliferation of host T-helper (TH) cells and which grow progressively in the peripheral lymphoid tissues of immunocompetent recipients. However, tumor growth is compromised in immunosuppressed syngeneic recipients, suggesting that the host response to SJL follicular center cell (SJL/FCC) lymphoma cells is required for optimal tumor growth. In vitro studies indicate that the host TH cells (Lyt-1+, 2-, L3T4a+) which respond to the major histocompatibility complex (MHC) class II (I-As) surface determinants on the SJL/FCC lymphoma cells produce a variety of lymphokines, some of which may promote tumor growth in vivo. The results of this study demonstrate that treatment of lymphoma-injected mice with L3T4a-specific mAb inhibits the growth of the SJL/FCC lymphoma cells, despite the fact that these tumor cells do not express L3T4a determinants. Thus, in this model, mAb therapy targeting host immune cells rather than the tumor cells is an effective means to control tumor growth. Long-term observation of SJL/FCC lymphoma-injected, anti-L3T4a mAb-treated mice reveals prolonged survival of the majority of these animals with periodic recurrence of tumor growth. During periods of remission, LN cells from these long-term surviving animals were unable to mount the characteristic in vitro host response to irradiated SJL/FCC lymphoma cells. These results provide direct evidence that SJL/FCC lymphoma cells fail to retain their characteristic neoplastic properties in a microenvironment that is initially devoid of tumor-responsive TH cells.

Characterization and growth factor requirements of SJL lymphomas. II. Interleukin 5 dependence of the in vitro cell line, cRCS-X, and influence of other cytokines

Follicular B cell lymphomas of SJL mice [reticulum cell sarcoma (RCS)] are dependent on syngeneic Ly-1+,2- T cells for their growth. These T cells produce a number of lymphokines in response to stimulation with gamma-irradiated RCS cells including interleukin (IL) 2, interferon-gamma (IFN-gamma), IL4 and IL5, some of which may be required for growth of the tumor. Previous studies have shown that an RCS cell line, cRCS-X, can be maintained in vitro indefinitely, if the cultures are supplemented with gamma-irradiated lymph node (LN) cells or with a preparation of human B cell growth factor (BCGF). In the present studies, the growth requirements of this cell line were analyzed in more detail in short-term assays of both [3H]thymidine incorporation and colony formation in agarose. Recombinant murine IL5 cause dose-dependent proliferation of cRCS-X cells similar to that induced with BCGF. The level of colony formation by cRCS-X cells induced by optimal concentrations of BCGF was not increased further by the addition of IL5, suggesting that the two factors act via a common mechanism. IL1 and IFN-gamma each enhanced cRCS-X proliferation induced by BCGF or IL5 in both assays. The effects of IL1 plus BCGF, IFN-gamma plus BCGF, and IL1 plus IL5 were clearly synergistic. Preincubation of cRCS-X cells with IL1 enhanced their ability to proliferate in response to BCGF or IL5 in [3H]thymidine incorporation assays, but the reverse sequence of cytokine addition showed no effect of IL1. No such effect was seen with IFN-gamma. Indeed, IL1 and IFN-gamma appeared to affect BCGF-induced cRCS-X growth by different mechanisms and their combined effects were greater than that of IL1 or IFN-gamma added separately. None of the other cytokines studied, including IL2, IL3, IL4, IL6, tumor necrosis factor-alpha, granulocyte monocyte-colony-stimulating factor or transforming growth factor-beta, had any detectable effect on cRCS-X cells, either alone or in combination with BCGF or IL5. Like IL5, SJL gamma-irradiated LN cells induced cRCS-X colony-forming units (CFU) in a dose-dependent manner. IL1, or the combination of IL1 plus IFN-gamma, clearly synergized with LN cells in the induction of cRCS-X CFU, suggesting that LN cells contribute IL5. The level of CFU induced by an optimal dose of BCGF was enhanced further in the presence of LN cells and IL1.(ABSTRACT TRUNCATED AT 400 WORDS)

In vivo growth inhibition of Ia+ lymphomas in SJL mice treated with I-As-reactive monoclonal antibody

SJL/J mice injected with a syngeneic, I-As-positive transplantable lymphoma (RCS) and treated with I-As-reactive monoclonal antibody (McAb) for one week showed reduced tumor growth in peripheral lymph nodes and spleen when compared to untreated controls. The effect of McAb on RCS growth was observed after treatment with I-As McAb derived from two different hybridomas, but similar growth inhibition did not occur in RCS-injected mice treated with a non-cross-reacting I-Ab McAb. Specificity of the effect was also indicated by the observation that partial absorption of I-As McAb with I-As-positive cells decreased its ability to reduce tumor growth in RCS-injected SJL recipients. In parallel experiments in which McAb treatment was stopped after one week, RCS-injected mice survived up to 8 times longer (80 days) than untreated control mice, which died by day 10 after tumor cell inoculation. Although the precise mechanism(s) by which McAb treatment influences RCS growth has not been fully characterized, it is likely that I-As McAb may block the characteristic T cell proliferative response to I-A antigens on RCS cells that appears necessary for progressive tumor growth in vivo. Absence of such host immune recognition could result in either a deficiency in production of RCS growth-promoting lymphokines or induction of effector cells capable of inhibiting tumor growth.

Proliferative responses of T cells from SJL----F1 and F1----SJL bone marrow chimeras to SJL lymphoma cells

RCS tumor cells induce marked proliferation of syngeneic SJL T cells in vivo and in vitro. Certain F1 hybrids of SJL mice give high proliferative responses to gamma-RCS, while other F1 hybrids give low responses. SJL----"non-responder" F1 and "non-responder" F1----SJL semiallogeneic bone marrow chimeras were prepared to study how the host environment affects the ability of T cells to give a proliferative response to gamma-RCS. The results indicate that T cells educated in an SJL host become responsive to RCS cells, while T cells educated in an (SJL X BALB/c)F1 host become unresponsive. This finding applies to both thymus and lymph node T cells. The unresponsiveness in F1 mice is not due to suppressor cells, since added F1 cells do not affect the proliferative response of SJL cells to gamma-RCS. Instead, it appears that RCS-specific T cells are either deleted in (SJL X BALB/c)F1 mice, or expanded in SJL mice as they develop. These findings are discussed in relation to the specificity of the responding T cells, for LPS activated syngeneic B cell blasts as well as RCS cells, and to the presence of a "leaky" thymus barrier in SJL mice for B cells.