Interleukin 1 secretion is not required for human macrophage support of T-cell proliferation

Interleukin 1 (IL-1) is a soluble factor secreted by stimulated monocytes (Mo) and animal macrophages (Mx). We have previously demonstrated that human Mo cultured in vitro for 1-6 days transform to Mx, and retain their ability to support concanavalin A (Con A)-driven T-cell proliferation. We have also shown that, paradoxically, these Mx do not secrete IL-1, when stimulated by endotoxin (LPS). In this study we examined two alternative hypotheses: T cells plus mitogen induce Mx IL-1 production, and human Mx deliver a second signal to T cells via a non-IL-1 mechanism. IL-1 was assayed in a mouse CD-1 thymocyte system without concanavalin A. Mo/Mx were cultured with T cells at low (2 X 10(4)/200 microliters) or high (1 X 10(5)/200 microliters) concentrations for 2 or 4 days, in the presence of Con A. Six hours prior to quantitation of proliferation, 50 microliters of supernatant was removed and assayed for IL-1. As expected both Mo and Mx enhanced T-cell proliferation eight- to tenfold. Mo secreted large amounts of IL-1; there was no demonstrable IL-1 activity present in supernatants from cultures containing either T cells and Mx, or Mx alone. Similar results were obtained by preincubating the cells (Mo, Mx, and T cells) with Con A for 12 hr and removing Con A prior to a 36-hr coculture. We examined the possibility that a small amount of IL-1 may be able to support Con A-stimulated T-cell proliferation and yet may not induce thymocyte proliferation. The highest dilutions of Mo supernatant (1:125) which supported T-cell proliferation also caused a fivefold increase in thymocyte proliferation. Supernatants from Mx failed to stimulate thymocyte proliferation or support Con A-driven T-cell proliferation. However, Mo and Mx lysates contain Il-1 activity. We conclude that human Mx support Con A-induced T-cell proliferation in the absence of IL-1 secretion. Mx may support T-cell proliferation by cell-bound IL-1 or by a non-IL-1 mechanism.     

Differential requirement for accessory cells in polyclonal T-cell activation

Highly purified rat Ia-negative (OX-6-) and Ia-positive (OX-6+) T cells were employed to examine the requirement for accessory cells (AC) and/or soluble factors in the activation of resting T cells with Con A, PHA, sodium periodate, or antigen. A variety of cells were employed as AC, including Ia-positive and Ia-negative macrophages (M phi), gamma-irradiated (2000 rad) or non-irradiated OX-6+ T cells, and several Ia-negative adenovirus-transformed rat embryo fibroblast cell lines. Our results suggested that for the expression of IL-2 receptors (IL-2R) and proliferation of OX-6- T cells in response to Con A, PHA, or antigen, there was an obligatory requirement for the presence of AC which could not be overcome by the addition of IL-1 and/or IL-2. Activation of OX-6- T cells with antigen required the presence of Ia+ AC, while activation with mitogens could be initiated with Ia- AC. M phi were efficient in AC function in all responses tested, while the AC function of OX-6+ T cells (TAPC) proved discriminatory under different conditions. The optimal response to PHA required much higher concentrations of TAPC as AC than for the Con A response. TAPC failed to stimulate sodium periodate-treated T cells under any conditions tested. Furthermore, when TAPC were employed as AC, their antigen-presenting ability was radiosensitive, while their AC function for Con A and PHA was radioresistant. These results suggest that molecules involved in T cell-AC interactions may differ, depending on the source of AC and/or type of the proliferative stimulus provided to T cells. This data has been discussed in the context of T-cell activation.     

Influence of Concanavalin A on 3-O-methylglucose uptake in cultured chick embryo fibroblasts. Evidence for differences related to the age of embryos

Concanavalin A (Con A) was found to inhibit hexose uptake in cultured fibroblasts derived from 8-day chick embryos and to stimulate this process in those derived from 16-day embryos. Con-A effects depended on the duration of contact with cells and lectin and were inhibited by alpha-methylmannopyrannoside. Con A was shown to mask about 70% of the hexose carriers in both 8- and 16-day embryo fibroblasts. Lectin altered the hexose uptake very rapidly. Con A only modified the Vmax of the uptake system and did not alter the Km. This indicates that either the number or mobility of hexose carriers were modified by Con-A treatment. The differential effect of lectin could be due to a modification of the hexose-carrier mobility during the embryonic differentiation of fibroblasts. Secondary effects may affect cell growth.     

Effect of corticosteroids on human in vitro anamnestic response.

When human peripheral blood lymphocytes were cultured in the presence of the antigens streptodornase (SKSD) and allogeneic lymphocytes (MLC), increased rates of DNA synthesis were observed 4 to 6 days laer. If these cell cultures were continued to 12 days, the rates of DNA synthesis returned to control levels. On rechallenging these cells with the same antigens, an accelerated response was observed. The corticosteroid preparations hydrocortisone and methylprednisolone suppressed both of these responses and also impaired the ability of the 12-day cultures to generate cells responsible for the accelerated secondary response. Although cells cultured for 12 days in the presence of SKSD and hydrocortisone responded poorly to SKSD rechallenge, they responded well in MLC. Hence, the suppressive effect was not completely unselective.     

Membrane-associated interleukin 1 is required for the activation of T cells in the anti-CD3 antibody-induced T cell response

To establish the role of the membrane-associated form of IL 1 in T cell activation, we tested the accessory function of monocytes (Mo) that were unable to secrete or release soluble IL 1. The data obtained show that strictly purified resting T cells start to proliferate in response to anti-CD3 antibody (OKT3) stimulation in the presence of paraformaldehyde (PFA)-fixed Mo or 3-day cultured Mo (macrophages). The findings that i) PFA-fixed Mo did not produce or release IL 1, ii) the accessory function of PFA-fixed Mo could be inhibited with pretreatment with anti-IL 1 antibody, iii) PFA-fixed Mo had a comitogenic effect in the murine thymocyte assay, and iv) there was a temporal difference between the capacities to function in the comitogenic assay and to produce soluble IL 1, suggest that human Mo can express membrane-associated IL 1 and that it is functionally relevant.     

IL-6 and IL-1 enhance the accessory activity of human blood monocytes during differentiation to macrophages

The role of IL-6 and IL-1 in the regulation of accessory activity and differentiation in the human monocyte/macrophage (Mo/Mph) system was investigated. IL-6 combined with IL-1 had a strong effect on the accessory activity of Mo-derived cells dependent on their state of differentiation in vitro. Fresh Mo prepared from peripheral blood differentiated into potent accessory cells in vitro within 24 h in the absence of exogenous triggers in serum-containing and serum-free medium. Mo cultured for 2 days in the presence of the cytokines IL-6 and IL-1 did not significantly increase their spontaneous accessory activity. However, the simultaneous addition of antibodies against IL-6 and IL-1 to accessory Mo cultures significantly diminished their T cell stimulatory capacity. These findings suggest an important positive feedback role of IL-6 and IL-1, secreted by Mo at this early state of differentiation. In marked contrast, untreated mature Mph generated in vitro from Mo exhibited a low spontaneous accessory potency. However, when these cells were subjected to IL-6 and/or IL-1, we observed a strong dose dependent increase in their potency to stimulate a T cell response. Parameters indicating the differentiation of Mo to Mph, such as acid phosphatase and 5' nucleotidase, were not influenced by the addition of IL-1, IL-6, or a mixture of both and confirmed the presence of mature Mph after 6 days of culture. Based on these observations, we conclude that the monocyte-derived cytokines IL-6 and IL-1 not only directly act on T cells but may also function as a signal for accessory activity during Mo/Mph differentiation.     

B-cell-derived interleukin 1 (IL-1)-like factor. I. Relationship of production of IL-1-like factor to accessory cell function of Epstein-Barr virus-transformed human B-lymphoblast lines

The relationship of production of interleukin 1 (IL-1)-like factor to accessory function of Epstein-Barr virus (EBV)-transformed B lymphocytes was examined. Six of eight human EBV-B cell lines spontaneously produced and released detectable levels of thymocyte comitogenic factor in vitro, but no interleukin 2 (IL-2) activity. Eight of eight produced fibroblast proliferation activity. Culture supernatants from the two apparent nonproducers of thymocyte comitogenic activity induced the proliferation of the IL-1-dependent murine helper-T-cell clone D10G4.1 in the presence of concanavalin A (Con A). One of the EBV-B cell lines produced a potent inhibitory factor in addition to IL-1-like thymocyte comitogenic and fibroblast proliferation factors. The inhibitory factor inhibited mouse thymocyte proliferative response to Con A, and the proliferation of the IL-2-dependent CT6 cell line, but not human fibroblast growth. All but one of the eight EBV-B cell lines tested, the exception being the line that produced an inhibitory factor, were able to serve as antigen-presenting cells that enabled purified human T lymphocytes to proliferate in one-way mixed lymphocyte reactions (MLR) and in response to Con A. The supernatants of 14 of 16 clones derived from two of the EBV-B cell line cells contained thymocyte comitogenic activity and all 16 stimulated fibroblast proliferation. The phenotypic characteristics of the EBV-B cell lines were heterogeneous, but there was no clear-cut relationship between the cell surface phenotypes of either the cloned or uncloned EBV-B cells and their ability to produce these factors. These studies show that all of the EBV-B cell lines that can function as accessory cells have the capacity to produce an IL-1-like factor.     

Signals involved in T cell activation. I. Phorbol esters enhance responsiveness but cannot replace intact accessory cells in the induction of mitogen-stimulated T cell proliferation

The role of accessory cells (AC) in the initiation of mitogen-induced T cell proliferation was examined by comparing the effect of intact macrophages (M phi) with that of 4-beta-phorbol 12-myristate 13-acetate (PMA). In high-density cultures, purified guinea pig T cells failed to proliferate in response to stimulation with phytohemagglutinin (PHA), concanavalin A (Con A), or PMA alone. The addition of M phi to PHA or Con A but not PMA-stimulated cultures restored T cell proliferation. The addition of PMA to high-density T cell cultures stimulated with PHA or Con A also permitted [3H]thymidine incorporation, but was less effective than intact M phi in this regard. This action of PMA was dependent on the small number of AC contaminating the T cell cultures as evidenced by the finding that PMA could not support mitogen responsiveness of T cells that had been depleted of Ia-bearing cells by planning, even when these cells were cultured at high density. When PMA was added to T cell cultures supported by optimal numbers of M phi, catalase-reversible suppression of responses was noted. Even in cultures containing catalase, PMA failed to enhance responsiveness above that supported by optimal numbers of M phi. A low-density culture system was used to examine in greater detail the possibility that PMA could completely substitute for M phi in promoting T cells activation. In low-density cultures, mitogen-induced T cell proliferation required intact M phi. PMA could not support responses even in cultures supplemented with interleukin 1-containing M phi supernatants or purified interleukin 2 alone or in combination. Similar results were found in high-density cultures of T cells depleted of Ia-bearing cells. These results support a model of T cell activation in which AC play at least two distinct roles. The initiation of the response requires a signal conveyed by an intact M phi, which cannot be provided by either a M phi supernatant factor or PMA. The response can be amplified by additional M phi or M phi supernatant factors. PMA can substitute for M phi in this regard and can provide the signal necessary for amplification of T cell proliferation supported by small numbers of intact AC.     

Abnormal activation and loss of suppressor T cells in the spontaneously hypertensive rat.

Suppressor T cell function in the spontaneously hypertensive rat (SHR) and normotensive Wistar Kyoto (WKY) rats was analyzed using syngeneic mixed lymphocyte reaction (SMLR) and concanavalin A (Con A) activation. A depressed SMLR was found in adult SHR but not in adult WKY. IL-2 synthesized by SHR was 40-fold lower than that of WKY, and the suppressor T cells generated in the SMLR were incapable of suppressing IgG synthesis. Precursors of cells that can be activated by Con A to become functional suppressor cells are reduced in adult SHR. Supernatant fluids derived from Con A-activated spleen cells from adult SHR failed to significantly inhibit IgG synthesis by cultures of syngeneic spleen cells compared to supernatant fluids from young SHR or WKY Con A-activated spleen cells. However, spleen cells from both adult SHR and WKY proliferated strongly and released equivalent amounts of IL-2 in response to Con A. Addition of exogenous IL-2 to the SMLR cultures in vitro restored the ability of SHR T cells to respond in the SMLR, with generation of cells capable of suppressing IgG synthesis. Administration of SHR with IL-2 in vivo also restored the suppressor T cell function in the SMLR. These results suggest a defective suppressor T cell activation and loss of suppressor T cell activity as the SHR age.     

Accessory cell competence of ovine oligodendrocytes in mitogenic activation of human peripheral T cells

The multiple sclerosis (MS) plaque is characterized by mononuclear inflammatory cell infiltration, demyelination, loss of oligodendrocytes (OGC), and proliferation of astrocytes. Although antigen-specific, Ia-dependent cellular immune mechanisms have been sought in plaque pathogenesis, Ia-independent T cell activation has not been actively investigated. We examined a potential role of OGC in accessory cell-dependent T cell mitogenesis with the anti-T3 monoclonal antibody OKT3. OGC isolated from ovine white matter on sucrose density gradients were uniformly negative for esterase activity, unlike ovine monocytes. Purified human T cells did not exhibit significant proliferation in 3-day cultures with OKT3, autologous peripheral blood adherent cells (PBAC), or ovine OGC. When T cells were cultured with either PABC or OGC in the presence of OKT3, brisk mitogenesis was observed. Thus, OGC have the capacity to function as accessory cells in the mitogen-induced proliferation of T cells.     

Influence of Concanavalin A on 3-O-methylglucose uptake in cultured chick embryo fibroblasts

Abstract. Concanavalin A (Con A) was found to inhibit hexose uptake in cultured fibroblasts derived from 8-day chick embryos and to stimulate this process in those derived from 16day embryos. (1) Con-A effects depended on the duration of contact with cells and lectin and were inhibited by α-methylmannopyrannoside. (2) Con A was shown to mask about 70% of the hexose carriers in both 8- and 16-day embryo fibroblasts. Lectin altered the hexose uptake very rapidly. (3) Con A only modified the V^max of the up- take system and did not alter the K^m. This indicates that either the number or mobility of hexose carriers were modified by Con-A treatment. The differential effect of lectin could be due to a modification of the hexose-carrier mobility during the embryonic differentiation of fibroblasts. Secondary effects may affect cell growth.     

In vitro immune response of human peripheral lymphocytes. II. Properties and functions of concanavalin A-induced suppressor T cells.

Con A-stimulation of human peripheral T lymphocytes induced both suppressor and helper T cells. ConA-generated suppressor T cells inhibited PWM-induced IgG and IgM production in PBL. Lower concentrations of Con A (0.5 micrograms/ml) or shorter incubation periods (6 to 24 hr) induced mainly helper T cells, while higher concentrations of Con A (10 micrograms/ml) or longer incubation periods (at least 48 hr) induced suppressor T cells. Con A-generated suppressor T cells were sensitive to mitomycin treatment and exerted their suppressor function on the early phase of differentiation and/or proliferation of B cells but not on the final differentiation of B cells to Ig-producing cells. The identity of the MHC was not required for the expression of suppressor function. Suppressor T cells competed with helper T cells in PWM-induced Ig-production of PBL. This experimental system can be applied to estimate the regulatory function of T cells in several disease states.     

电剌大鼠的血清中淋巴细胞转化抑制因子的作用机制分析

Previous reports showed that EA stimulation (3V, 2Hz, 30 min/d, 5 d) induced the production of one or more lymphocyte proliferation-inhibitory factor(s) in the rat serum. In this paper, the mechanisms of the action for the inhibitory factor(s) to suppress lymphocyte proliferation were studied. (1) the lymphocytes from different immune organs of the mice were prepared and cultured with the rat serum stimulated by EA. The results show that the serum not only inhibited the mouse lymph node T cell proliferation induced by Con A, but also inhibited the mouse thymocyte and spleen T cell proliferation induced by Con A. When B cells were stimulated by LPS, the proliferative effect can also be inhibited significantly by the rat serum stimulated by EA. This implies that the effect of the lymphocyte proliferation-inhibitory factor(s) has no specificity. (2) Incubation of the mouse lymph node cell with serum for one hour is enough to cause an inhibitory effect on Con A stimulated lymphocyte proliferation. However, no inhibitory effect was observed if the mouse lymph node cells were incubated with Con A for 15 min or 30 min before the addition of rat serum. The results demonstrate that the lymphocyte proliferation-inhibitory factor(s) act on the early events of T lymphocyte activation induced by Con A. (3) Protein kinase C (PKC) is a key link in the activation of T and B lymphocyte proliferation by Con A and LPS respectively. So it would be interesting to learn whether the inhibitory effect of the lymphocyte proliferation-inhibitory factor(s) is caused by the inhibition of PKC activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

IL-1 serves as a secondary signal for IL-9 expression.

IL-9 is produced in vitro by activated CD4+ T cell lines of the Th2 subtype and by naive CD4+ T cells. Here we show that T cell lines stimulated with Con A in the presence of accessory cells (AC) such as irradiated spleen cells or bone marrow-derived macrophages produced substantially more IL-9 than T cells stimulated with Con A alone. These data suggest that AC influence the production of IL-9 through accessory signals that result in an at least 10-fold increase of IL-9 secretion by the respective T cells. Addition of IL-1 to T cells activated by Con A, PHA, or anti-CD3 antibodies revealed that this monokine was responsible for the potentiation of IL-9 production. This finding was confirmed by applying anti-IL-1 antibodies. The production of other lymphokines, namely, IL-3, IL-4, and IL-6, by activated T cells was not or only marginally enhanced in the presence of AC or IL-1, thus indicating that the synthesis of IL-9 is regulated differently from that of other Th2-derived lymphokines. Furthermore, it was demonstrated by Northern blot analysis that IL-1 increases IL-9 expression at the pretranslational level. Because IL-1 alone failed to induce the production of IL-9 by T cells, this monokine acts as a costimulator in combination with a T cell receptor-mediated signal.     

Ontogeny of proliferative and cytotoxic responses to interleukin 2 and concanavalin A in murine fetal thymus

The ontogeny of proliferative and cytotoxic responses to concanavalin A (Con A) and interleukin 2 (IL 2) in C57BL/6J (B6) fetal thymus (FT) was investigated. Embryonic thymocytes were either taken from embryos at different times of gestation or from 14 day B6 FT that were maintained as organ cultures for various times. It was found that the B6 FT could proliferate to Con A and EL4 SN (an IL 2 containing culture supernatant) in a synergistic fashion. This synergy between Con A and EL4 SN was first observed at the 16th to 17th day of gestation. A similar differentiation process took place in 14-day FT that had been maintained as organ cultures; the synergy between Con A and EL4 SN was first observed after 3 days in organ culture. This synergy increased with increasing time of organ culture, and was most evident after 10 days. The synergy between Con A and EL4 SN was also observed when the EL4 SN was replaced with IL 2 which had been purified from crude EL4 SN to apparent homogeneity. B6 FT could also form cytotoxic T lymphocytes (CTL) on stimulation with Con A and EL4 SN. Con A-activated CTL (polyspecific) were detected by including phytohemagglutinin in the assay medium. CTL response was first detected in the 17-day fetal thymus by using this assay. In organ cultures, CTL responses were first detected after 4 days in organ culture, and reached peak levels after 12 to 14 days. The CTL precursor (CTL-P) frequencies in the B6 FT after 2, 5, 10, and 14 days in organ culture were less than 1/10,000, 1/2232, 1/297, and 1/70, respectively; the corresponding CTL-P frequency in adult thymus was 1/60. After 6 days in organ culture, B6 FT could also form CTL in response to Con A and pure IL 2. This finding suggests that the ability to synthesize other differentiation factors that are required for CTL responses is acquired at an early time of thymic differentiation.     

Lyt-2+ cells. Requirements for concanavalin A-induced proliferation and interleukin 2 production

The requirements for inducing Lyt-2+ T cell proliferation in response to concanavalin A (Con A) were examined. Purified Lyt-2+ or L3T4+ spleen cells of C57BL/6 origin were stimulated with Con A and syngeneic macrophages (MO) in the presence of monoclonal antibodies to T cell markers or to polymorphic determinants on major histocompatibility complex molecules, and assessed for the ability to proliferate and to produce interleukin (IL) 2. alpha I-Ab failed to inhibit the Con A response of Lyt-2+ cells at dilutions that significantly inhibited the response of L3T4+ cells. In contrast, alphaKb/Db or alpha Lyt-2.2 specifically inhibited the response of Lyt-2+ cells, but not L3T4+ cells. The ability of alpha Kb/Db and of alpha Lyt-2.2 to inhibit the response of Lyt-2+ cells was dependent upon the concentration of Con A. These data demonstrate that optimal triggering of T cell subsets to proliferate and to produce IL-2 in response to Con A requires interactions with the appropriate restricting major histocompatibility complex molecule. The role of accessory cells in Lyt-2+ Con A-induced proliferation and IL-2 production was also investigated. Purified Lyt-2+ cells and purified L3T4+ cells failed to respond to Con A in the absence of MO. IL-1 reconstituted the response when MO were limiting, but failed to restore the response of either Lyt-2+ or L3T4+ cells when T cells were rigorously purified to remove all MO. These results demonstrate that triggering Lyt-2+ T cells, like L3T4+ T cells, requires accessory cells, and that this does not merely reflect a requirement for IL-1 production. Thus, Con A-induced proliferation and IL-2 production by Lyt-2+ T cells requires intimate contact with accessory cells and interactions dependent upon the class I-restricting element.     

Lymphocyte function in experimental African trypanosomiasis. VIII. Loss of suppressor T cell function in lymph nodes

The immunosuppression that occurs in mice experimentally infected with African trypanosomiasis has been examined further. In the present study we have examined lymph node cells from Trypanosoma rhodesiense-infected C57Bl/6J mice for the ability to produce mitogen induced antigen-nonspecific suppressor T cells (Ts). Inguinal, mesenteric, and brachial lymph node cells were harvested from uninfected control mice and from mice at different periods of infection. These cells were cultured with or without concanavalin A (Con A) for 48 hr to induce Ts activity. After stimulation, the control and infected lymph node cells were passed over Sephadex G-10 columns to remove suppressor macrophages that arise during the infection from Con A-induced Ts. The column passed cells were then added to normal mouse responder spleen cells in a primary in vitro antibody response culture system with sheep erythrocytes (SRBC) as antigen. The resultant plaque-forming cell responses to SRBC indicated that Ts function was not induced in infected lymph node cell populations. However, early in the infection, a stimulatory signal was provided by both the untreated and Con A-treated infected lymph node cells, which was lost in the terminal stage. Determinations of T cell subpopulations revealed that the infected Lyt 2.2-bearing subpopulation was not significantly altered from normal controls. We conclude that T. rhodesense infected mice fail to mount normal lymph node cell antigen nonspecific Ts responses and that this loss of activity may be due to an intrinsic dysfunction in the suppressor T cell population.     

The anti-T cell monoclonal antibody 9.3 (anti-CD28) provides a helper signal and bypasses the need for accessory cells in T cell activation with immobilized anti-CD3 and mitogens

CD28 is an antigen of 44 kDa which is expressed on the membrane of the majority of human T cells. The present study examines the functional effects of an anti-CD28 monoclonal antibody (mAb 9.3) on T cell activation induced with immobilized anti-CD3 mAb OKT3 or with mitogens, in the absence of accessory cells. To this end, we used blood resting T cells that were completely depleted of accessory cells (monocytes, B cells, and natural killer cells), and consequently did not respond to recombinant interleukin-2 (rIL-2), to immobilized OKT3, to PHA, or to Con A. Addition of mAb 9.3 to the cultures enhanced IL-2 receptor expression (Tac antigen) on PHA- or immobilized OKT3-stimulated T cells and induced IL-2 receptors on Con A-stimulated T cells. Moreover, addition of mAb 9.3 to cultures of T cells stimulated with PHA, Con A, or immobilized OKT3 resulted in IL-2 production. Soluble mAb 9.3 was a sufficient helper signal for T cell proliferation in response to PHA or immobilized OKT3. Crosslinking of mAb 9.3 by culture on anti-mouse IgG-coated plates enhanced the helper effect and was an essential requirement for the induction of T cell proliferation in response to Con A. No other anti-T cell mAb (anti-CD2, -CD4, -CD5, -CD7, -CD8) was found to provide a complete accessory signal for PHA or Con A stimulation of purified T cells. T cell proliferation induced by the combination of PHA and mAb 9.3 was strongly inhibited by the anti-IL-2 receptor mAb anti-Tac. In conclusion, mAb 9.3 can provide a signal bypassing monocyte requirement in T cell activation with immobilized OKT3, PHA, and Con A, resulting in an autocrine IL-2-dependent pathway of proliferation.     

Inhibition of in vitro T cell activation by corneal endothelial cells.

Cells and tissues of the anterior uvea and aqueous humor express activities which inhibit immune responses. These activities include soluble factors such as TGF-beta and uncharacterized cell surface interactions. Relatively little is known regarding the immunologic activities of corneal endothelium, despite its potentially important role in contributing to the immune privilege of the anterior chamber and the high success rate of corneal transplantation. In this report, in vitro studies of cultured rat corneal endothelial (CE) cells were done using S-antigen-specific LEW rat T cell lines, or S-antigen-specific T cell hybridomas, to examine the immunologic capabilities of CE cells. Monolayers of LEW rat CE cells were unable to present antigen or a mitogen, Con A, to T cell lines or hybridomas as assessed by the lack of a proliferative response or IL-2 secretion. Furthermore, the CE cells exerted a potent inhibitory effect when added to in vitro proliferation assays of T cell lines stimulated with antigen or Con A. When T cells were preactivated on conventional antigen presenting cells and then transferred to wells containing CE cells, their proliferation was not inhibited. Although CE cells inhibited activation of T cell lines and hybridomas, they did not inhibit the growth of T cell hybridomas or CTLL cells, nor did the CE cells adversely affect the viability of resting T cells cultured on CE monolayers. The inhibitory effect was reversible as preincubation of T cells on CE cells for up to 6 days followed by washes restored T cell responsiveness when assayed on splenocytes. The inability to stimulate proliferative responses was not affected by preincubation of the CE cells with lymphokines which increase MHC antigen expression. The inhibition observed in these assays was not MHC-restricted as CE cells from both LEW and BN rats were equally inhibitory. CE cells from rabbits and cats were also potent inhibitors of T cell activation, suggesting that the mechanism is evolutionarily conserved. The mechanism of inhibition of CE cells is unknown at this time.     

Stimulation of mouse lymphocytes by a mitogen derived from Mycoplasma arthritidis. IV. Murine T hybridoma cells exhibit differential accessory cell requirements for activation by M. arthritidis T cell mitogen, concanavalin A, or hen egg-white lysozyme

A T-cell mitogen present in culture supernatants of Mycoplasma arthritidis (MAS) is known to exhibit an absolute dependence on E alpha-bearing accessory cells (AC), which appear to function by binding the mitogen. We therefore compared the specificity and nature of the AC requirements for MAS and antigen-induced production of IL 2 in T hybridoma cell lines originating from a fusion by using hen egg-white lysozyme (HEL)-specific, H-2d-restricted T blasts. A marked specificity was noted in the ability of the hybridoma lines to become activated by Con A, MAS, or HEL antigen. Thus all three lines produced IL 2 in response to Con A without the addition of B lymphoma AC. Two lines responded to MAS, but only in the presence of AC, and only one line responded to HEL antigen in the presence of AC. Using the HEL responsive T hybridoma line, we demonstrated that disrupted AC and AC membranes could present MAS but not HEL. MAS rapidly associated with AC at 4 degrees C, whereas HEL failed to do so. Paraformaldehyde-fixed AC could absorb the mitogen in MAS and present it to T hybridoma cells within several minutes, whereas HEL antigen could only be presented by fixed AC if there was a prolonged period of incubation (greater than 30 min) at 37 degrees C before fixation. The combined data indicate that metabolically active cells are not required for the association of MAS with AC or for presentation of MAS to T hybridomas. In contrast, HEL antigen requires metabolically active cells for both of these processes. Thus, the mitogen in MAS can bind to AC without any processing requirements, and it is likely that the resulting complex of mitogen and Ia molecules can directly activate T hybridoma cells.