Host-tumor interactions in the SJL lymphoma model

From Cell Culture to Organoids-Model Systems for Investigating Prion Strain Characteristics

Prion diseases are the hallmark protein folding neurodegenerative disease. Their transmissible nature has allowed for the development of many different cellular models of disease where prion propagation and sometimes pathology can be induced. This review examines the range of simple cell cultures to more complex neurospheres, organoid, and organotypic slice cultures that have been used to study prion disease pathogenesis and to test therapeutics. We highlight the advantages and disadvantages of each system, giving special consideration to the importance of strains when choosing a model and when interpreting results, as not all systems propagate all strains, and in some cases, the technique used, or treatment applied, can alter the very strain properties being studied.

Pathogenesis of Human Reactive-Appearing «Non-Monomorphous» Malignant Lymphoproliferative Disorders: A Hypothesis

Human reactive-appearing « non-monomorphous » malignant disorders, such as Hodgkin's disease, T-cell-rich B-cell lymphomas and angioimmunoblastic lymphadenopathy display a peculiar and unifying characteristic, which biologically differentiates them from « monomorphous » non-Hodgkin's lymphomas. It consists in the coexistence within the pathologic tissue of a polyclonal, normal-appearing, presumed reactive cellular component, mainly composed of T-lymphocytes together with a clonal cell component constituting a minority of the pathologic mass. To explain the long-lasting coexistence of such polymorphic cell populations in the pathologic tissue of synchronous and metachronous localizations of the disease, it is hypothesized that they are interconnected by « biological interactions » which determine and sustain the pathologic process. Based on the biological characteristics of an experimental model (the follicular center cell « lymphoma » of the SJL murine strain), it is suggested that these human « non-monomorphous » malignant diseases should be regarded as a continuous spectrum of lymphoproliferative disorders sustained by a biological loop which interconnects different cell populations able to stimulate each other for growth.

Fukuoka-1 strain of transmissible spongiform encephalopathy agent infects murine bone marrow-derived cells with features of mesenchymal stem cells

BACKGROUND

The possible risk of iatrogenic transmissible spongiform encephalopathies (TSEs, prion diseases) from transplantation of marrow-derived mesenchymal stem cells (MSCs) is uncertain. While most cell lines resist infection, a few propagate TSE agents.

STUDY DESIGN AND METHODS

We generated MSC-like (MSC-L) cell cultures from bone marrow (BM) of mice inoculated with the human-derived Fukuoka-1 (Fu) strain of TSE agent. Cultured cells were characterized for various markers and cellular prion protein (PrP(C) ) by fluorescence-activated cell sorting and for PrP(C) and its pathologic TSE-associated form (PrP(TSE) ) by Western blotting (WB). Cell cultures were tested for their susceptibility to infection with Fu in vitro. The infectivity of one Fu-infected cell culture was assayed in mice.

RESULTS

BM cells from Fu-infected mice expressed neither PrP(C) nor PrP(TSE) after 3 days in culture as demonstrated by WB. Cells adherent to plastic and maintained under two different culture conditions became spontaneously immortalized and began to express PrP(C) at about the same time. One culture became transformed shortly after exposure to Fu in vitro and remained persistently infected, continuously generating PrP(TSE) through multiple passages; the infectivity of cultured cells was confirmed by intracerebral inoculation of lysates into mice. Both persistently TSE-infected and uninfected cells expressed a number of typical MSC markers.

CONCLUSION

BM-derived MSC-L cells of mice became persistently infected with the Fu agent under certain conditions in culture-conditions that differ substantially from those currently used to develop investigational human stem cell therapies.

Persistent propagation of variant Creutzfeldt-Jakob disease agent in murine spleen stromal cell culture with features of mesenchymal stem cells

The transmission of variant Creutzfeldt-Jakob disease (vCJD) through blood transfusions has created new concerns about the iatrogenic spread of transmissible spongiform encephalopathies (TSEs)/prion diseases through blood and plasma-derived products and has increased the need to develop efficient methods for detection of the agent in biologics. Here, we report the first successful generation of spleen-derived murine stromal cell cultures that persistently propagate two mouse-adapted isolates of human TSE agents, mouse-adapted vCJD, and Fukuoka 1. These new cell cultures can be used efficiently for studies of the pathogenesis of the disease, for development of diagnostics and therapeutics, and as a rapid ex vivo assay for TSE inactivation/removal procedures.

Protease-resistant prion protein in lymphoreticular tumors of variant Creutzfeldt-Jakob disease mice

We report protease-resistant prion protein (PrPres) in spontaneous lymphoreticular tumors of mice infected with the agent of variant Creutzfeldt-Jakob disease (vCJD). PrPres may accumulate in lymphoreticular system tumors of asymptomatic persons with vCJD. The statistical power of estimates of vCJD prevalence might be increased by expanding screening to include samples of lymphoreticular neoplasms.

META-controlled env-initiated transcripts encoding superantigens of murine Mtv29 and Mtv7 and their possible role in B cell lymphomagenesis

Spontaneous germinal center (GC)-derived B cell lymphomas of SJL mice (RCS) transcribe a 1.8-kb Mtv-29 mRNA under control of the META-env promoter. The encoded vSAg29 stimulates syngeneic Vbeta16(+) CD4(+) T cells, thereby acquiring T cell help necessary for RCS growth. Other strains of B cell lymphoma-prone mice include Mtv29(+) C57L and MA/MyJ, and the Mtv29(-) Mtv7(+)-recombinant inbred strain, SW x J-1. The lymphomas of these mice produce similar mouse mtv-vSAg-encoding mRNA, as characterized by Northern blotting, PCR, and RNase protection. A 1.8-kb mRNA in C57L/J and MA/MyJ lymphomas hybridized with an Mtv29-specific oligonucleotide, whereas SW x J-1 lymphomas produced 1.8-kb transcripts hybridizing with an Mtv7-specific oligonucleotide. Similar META-env-initiated transcripts were absent from LPS-activated B cells from any strain examined but were detected in Peyer's patch RNA from SJL mice. Like typical SJL-derived RCS, all these lymphomas stimulated syngeneic CD4(+) T cells and Vbeta16(+) T hybridoma cells. Immunohistochemical staining of primary tumors showed the presence of peanut agglutinin binding (PNA(+)) highly mitotic lymphoblasts, suggesting their GC derivation. The findings indicate that this novel mRNA for Mtv29 is present in B cell lymphomas from several Mtv29(+) mouse strains. Additionally, this is the first description of the ability of Mtv7 to produce transcripts that are controlled and spliced identically to those of Mtv29 and that are expressed in SW x J-1, I-A(s+), lymphomas that also stimulate Vbeta16(+) T cells. Our results suggest an important role for mouse mtv-vSAgs and Vbeta16 T cell stimulation in the development of GC-derived murine B cell lymphomas.

Requirement for reverse immune surveillance for the growth of germinal center-derived murine lymphomas

The concept of reverse immune surveillance, first conceived over 12 years ago, described the relationship that existed between germinal center-derived B cell lymphoma cells and the host immune system in SjL/J mice. According to reverse immune surveillance, recognition of tumor cell antigens and a response by the host immune system is required for tumor growth. The phenomenon of reverse immune surveillance related to B cell lymphomas has recently also been characterized in another inbred mouse strain, C57L/J. Moreover, elements of reverse immune surveillance have been observed in several other mouse strains that develop B cell lymphomas, suggesting that this lymphomagenic mechanism may be more common than first envisioned. In SJL and C57L mice, the B lymphoma cells express an MMTV-encoded superantigen (vSAg29) that stimulates syngeneic CD4+ T cells bearing Vbeta16 in their TCR. In contrast to the mRNAs for other MMTVs in normal mouse B cells, vSAg29 mRNA initiates in the env (META) region, undergoes splicing in the 3' env region, and continues through the 3' LTR. Copious cytokine production, including IFN-gamma, IL-4 and IL-5 accompanies the response of the T cells to this vSAg. In addition to cytokines produced by vSAg-responsive T cells, more recent evidence indicates that another cytokine, LTalphabeta2, which is expressed on the lymphoma cell surface, also plays a role in the promotion of the B cell lymphoma growth. It is possible that interaction with LTbeta-R on follicular dendritic cells or other stromal elements facilitates tumor growth by preventing apoptosis of the malignant B cells. To what degree these findings in the mouse are relevant to the development and/or growth of human B lymphoma cells remains to be determined. However, endogenous retroviral sequences do exist in the human genome. Interestingly, some of these sequences are homologous to MMTV, and are transcribed in B lymphoblastoid cells. Moreover microorganisms that are infectious for human B cells, such as EBV and Herpes Virus 8, may also produce superantigens.

B cell lymphomas of C57L/J mice; the role of natural killer cells and T helper cells in lymphoma development and growth

The Hodgkin's-like Type B neoplasms which arise spontaneously in aging C57L mice (25% incidence at 21 months of age) were first reported over 40 years ago, but since then relatively little has been published about these lymphomas. Based on previous studies in SJL mice, we investigated the phenotypic and functional properties of C57L-derived lymphomas in relation to Mtv29-encoded vSAg expression by the tumor cells, and their ability to stimulate TCR Vbeta-restricted T cells. The cell surface phenotype of the C57L lymphomas indicates a B cell origin (sIg(+), MHC II(+)). These B lymphoma cells also express co-stimulatory molecules [B7-1 (CD80) and HSA (CD24)], and stimulate marked proliferation of syngeneic CD4(+) T cells. C57L B lymphoma cells exhibit Mtv-encoded mRNA by northern analysis, and also stimulate IL-2 production from Vbeta16(+) T cell hybrids, suggesting a role for Mtv 29 in this syngeneic T cell response. After transfer to syngeneic recipients, primary C57L lymphomas grow slowly, if at all. However, tumor growth is greatly accelerated by pretreatment of C57L recipients with anti-asialo GM1 antibody (but not anti-CD8 mAb), suggesting that NK cells play a major role in inhibiting lymphoma growth. If, in addition to anti-asialo GM1, the mice are also pretreated with anti-CD4 mAb, tumor growth is markedly inhibited, indicating that the lymphoma-responsive syngeneic CD4(+) T cells promote tumor growth. Therefore, although the vSAg-induced response stimulated by vSAg29 expressing lymphoma cells in syngeneic TCR Vbeta-restricted CD4(+) T cells is an important etiologic factor in this type of B cell neoplasm both in C57L and in SJL mice, the final outcome of the spontaneous neoplastic process appears strongly influenced by endogenous NK activity in aging mice.

Spontaneous myopathy in the SJL/J mouse: pathology and strength loss

Myopathy has been found to develop spontaneously in 100% of SJL/J mice between 6 and 8 months of age. Extent of muscular involvement and mouse strength were quantified in SJL/J mice and Balb/c control mice 2-16 months old. Muscle from young SJL/J mice exhibited histopathological abnormalities and occasional inflammatory infiltrate. By 6 months, 78% of SJL/J mice had developed active myopathy. By 8 months, all SJL/J mice examined had active disease with a mean of 12.9% of muscle fibers affected. Replacement of muscle fibers by fat and/or collagen began at 10 months and was pronounced by 14 months. Significant decreases in strength scores (total body pulling force) at 6 months and 10 months of age reflected the onset of active myopathy and the onset of muscle degeneration, respectively. The spontaneous onset and 100% incidence of myopathy in the SJL/J mouse line should provide a useful model for idiopathic myopathy.

Mutagenesis associated with nitric oxide production in transgenic SJL mice

We recently reported development of an experimental model for the study of nitric oxide (NO.) toxicology in vivo. SJL mice were injected with superantigen-bearing RcsX (pre-B-cell lymphoma) cells, which migrated to the spleen and lymph nodes, where their rapid growth induced activation of macrophages to produce large amounts of NO. over a period of several weeks. In the experiments described here, we used this model to investigate mutagenesis in splenocytes exposed to NO. during RcsX cell growth. Transgenic mice were produced by crossbreeding animals of the pUR288 transgenic C57BL/6 and SJL strains. RcsX cells were injected into F1 mice and NO. production was confirmed by quantification of urinary nitrate, the ultimate metabolite of NO. Mutant frequency in the lacZ gene of the pUR288 plasmid was determined in DNA isolated from spleen (target) and kidney (nontarget) tissues. A significant elevation in mutant frequency was found in the spleen, but not in the kidney, of tumor-bearing mice. Furthermore, increases in mutant frequency in the spleen as well as NO. production were abrogated by administration of N-methylarginine, a NO. inhibitor, to mice following injection of RcsX cells. These results indicate that NO. had mutagenic activity in RcsX tumor-bearing mice and thus support a possible role for its involvement in the carcinogenic process.

Cyclophosphamide treatment of an SJL murine B-cell lymphoma increases the proportion of suppressive CD8+ over tumor-stimulatory CD4+ T-lymphocytes

Lymphomas (formerly reticulum cell sarcomas (RCS)) which develop spontaneously in SJL mice are a murine counterpart of human low grade B-cell non-Hodgkin's lymphoma. Tumor cells stimulate proliferation of syngeneic CD4+ T-lymphocytes which secrete cytokines required for tumor growth. Cyclophosphamide treatment of tumor-bearing mice (RCS/Cy) decreases in vitro tumor-stimulated CD4+ T-cell proliferation and, in turn, tumor growth, in part, through the suppressive action of CD8+ T-lymphocytes. In RCS/Cy compared to untreated tumor-bearing (RCS5) mice we report marked in vivo decreases in: (1) the activation (CD44HI/CD45RBLO phenotype) and proliferation (S + G2M phases of the cell cycle) of CD4+ T-lymphocytes; (2) the ratio of activated and/or proliferating CD4+ to CD8+ T-lymphocytes, and; (3) the proliferation of tumor cells. Also, depletion of CD8+ T-lymphocytes from RCS/Cy mice abrogated much of the efficacy of the RCS/Cy treatment and led to changes in lymphoid populations more reminiscent of those in RCS5 than RCS/Cy mice. The data support our hypothesis that the RCS/Cy treatment achieves its efficacy by preventing the predominance of CD4+ over CD8+ T-lymphocytes which is essential to maximum tumor growth in RCS5 mice. The results imply that analogous B-cell lymphomas in humans also may be treatable by shifting the T-cell balance toward inhibitory CD8+ rather than the tumor-stimulatory CD4+ T-lymphocytes.

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.

Murine survival of lethal irradiation with the use of human umbilical cord blood

We have found that human umbilical cord blood (HUCB) will routinely protect mice exposed to lethal levels of irradiation. At the end of 50 days, over seventy percent (70%) of mice injected with HUCB survived 900 cGy or irradiation, which produced 100% deaths in the uninjected control animals. Moreover, there was some evidence that human colony stimulating factors further improved survival. Anti-Natural Killer cell (NK) antibody was utilized along with HUCB in these studies, however, Anti-NK cell serum alone had no radioprotective effect in mice. The studies reported here suggest the possibility of utilizing HUCB for immediate protection of humans from lethal irradiation.

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.

Paraproteins and primary lymphoma in SJL mice. I. Individuality of idiotypes on paraproteins

The isotype distribution and idiotypic determinants of paraproteins (PP) found in sera from aging SJL mice were studied. One or more PP were found in 79% of 9-11 month old mice; the isotypes were gamma 1 greater than or equal to alpha greater than or equal to gamma 2a much greater than gamma 3 much greater than gamma 2b. There was a significant tendency for the PP to occur in pairs or triplets, multiple PP being found in 35% of the mice without an evident association between any two isotypes. Rabbit anti-Id was prepared against four isolated PP, two gamma 1 and two gamma 2a. Inhibition of anti-Id-Id interaction was specific for the immunizing PP only and was absent with all other PP studied (8 gamma 1 and 10 gamma 2 PP) and with normal SJL Ig. It is concluded that SJL PP fail to exhibit cross-reactive idiotypes and show a wider range of isotype distribution than was previously suspected, although PP of mu, delta, and epsilon isotypes are absent.

Production of human to mouse xenografts by umbilical cord blood

Utilizing human umbilical cord blood, it has been possible to create in irradiated animals a human to mouse xenograft. To facilitate hematopoietic reconstitution, SJL/J mice, which are functionally low in natural killer (NK) cells, were treated with anti-Asialo GM1 antibodies (anti-NK) and irradiation prior to injection of cord blood mononuclear cells. In contrast, SJL/J mice with the "beige" (bg/bg) mutation, which confers a functional NK cell deficiency, required only irradiation for successful transplantation. Human cells, detected by means of DNA probes, were demonstrated in the lungs and lymph nodes of irradiated animals up to 6 months after injection of the human cord blood cells.

CD8 suppressor cell activity and its effect on CD4 helper cell-dependent growth of SJL/J B-cell lymphomas

CD8 cells, flow cytometrically sorted from the lymph nodes of tumor-bearing and normal SJL/J mice, suppressed in vitro proliferation of syngeneic CD4 cells in response to concanavalin A, two independent SJL/J lymphomas, and LPS-activated syngeneic B-cell blasts. The data confirm earlier reports that nonspecific suppressor cells are generated as a consequence of SJL/J lymphoma-stimulated T-cell proliferation. Earlier reports are extended, in that the suppressor cell is identified as expressing CD8, and the suppressor activity is shown to decrease the tumor-stimulated CD4 cell proliferation which is essential to growth of these CD4-dependent murine B-cell lymphomas. In three separate experiments, anti-CD8 treatment of mice, in which CD4 cells were made limiting by injection with anti-CD4, increased growth of transplantable SJL/J lymphomas with corresponding increases in numbers of CD4 cells. The data imply that, under certain conditions, CD8 suppressor cells measurably influence growth of SJL/J lymphomas by regulating the tumor-stimulated CD4 cell proliferation essential to maximum growth of SJL/J lymphomas.

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)