Antigen presentation by hapten-specific B lymphocytes. V. Requirements for activation of antigen-presenting B cells

Splenic B cells specific for the haptens, 2,4,6-trinitrophenyl (TNP) or fluorescein isothiocyanate (FITC) were cultured with a range of concentrations of unmodified or TNP- or FITC-conjugated conalbumin and the conalbumin + I-Ak-specific, interleukin (IL) 1-dependent helper T cell clone, D10 . G4, in the presence and absence of IL-1. Lymphokine secretion, T cell proliferation, and antibody secretion by B cells all exhibited identical antigen dose responses. Thus, hapten-binding B cells presented low concentrations of haptenated conalbumin for activation of both the T and the antigen-presenting B cells. Whereas proliferation of D10 . G4 required the addition of IL-1, both lymphokine production and stimulation of B cells to antibody secretion occurred without exogenous IL-1. These results demonstrate that when B lymphocytes function as presenting cells for antigens that bind to their immunoglobulin receptors, activation of the responding T cells and the B cells themselves occur at similar concentrations of antigen. Moreover, for functional T-B interactions, antigen-presenting B and responding T lymphocytes constitute a complete system that requires no other accessory stimuli, whereas clonal expansion of T cells is dependent on accessory factors such as IL-1. Finally, since D10 . G4 secretes IL-4 but neither IL-2 nor interferon-gamma, our results demonstrate that differentiation of B cells as a consequence of direct ("cognate") interactions with helper T cells as well as of bystander B cells can occur in the absence of IL-1, IL-2, and interferon-gamma.     

Morphological aspects of lymphocyte-macrophage interactions in human tumoral effusions "in vivo" and "in vitro"

"In vivo" and "in vitro" morphological analysis of associations of cells ("rosettes") involved in immune response in human tumoral effusions revealed the existence of cell interactions either by simple membrane apposition between the cell projections or by gap-like junctions between two adjacent cells; endocytotic phenomena were also observed. The giant fibroblastic cells seen "in vitro" ("myofibronoblasts") reacting positively to anti-human macrophage Mabs, might be the cells presenting antigen to lymphocytes.     

Transfer of autoimmune encephalomyelitis with T lymphocytes in strain 13 guinea pigs

Experimental autoimmune encephalomyelitis (EAE) and/or tuberculin sensitivity were transferred to histocompatible recipients with myelin basic protein-stimulated and/or PPD stimulated guinea pig lymph node T cells previously separated by depletion of B cells ("panning") on rabbit anti-guinea pig Ig antibody-coated Petri plates. The depletion was augmented by complement-mediated lysis using mouse anti-guinea pig B-cell monoclonal antibody (31D2), rabbit anti-mouse Ig, and rabbit complement. B cells did not transfer EAE nor provide protection against active immunization with guinea pig spinal cord antigen.     

Characterization of suppressive immunoglobulin-binding factor (IBF). I. Production of IBF by a theta-positive lymphoma (L-5178-Y).

L-5178-Y, a theta-positive, Fc receptor-bearing mouse thymoma cell line spontaneously releases immunoglobulin-binding factor (IBF) upon short-term incubation in vitro. IBF produced by L-5178-Y cells is identical in its biologic activity with IBF produced by Fc receptor positive alloantigen-activated T cells. It suppresses the in vitro plaque response of mouse spleen cells to sheep erythrocytes by interfering mainly with the late phase of the generation of antibody-forming cells. Therefore, L-5178-Y thymoma affords a homogeneous source of IBF in sufficient quantities for the study of its biochemical nature and the mechanism by which it interferes with cells participating in antibody synthesis.     

In vitro and in vivo activated T cells display increased sensitivity to PGE2.

In this study we report that in vitro activation of T cells increased the cyclic AMP response to subsequent prostaglandin E2 (PGE2) stimulation severalfold per cell. This sensitization of T cells to PGE2-induced cyclic AMP generation was observed when the T cells had been stimulated in vitro for 5 days with either the CD3 monoclonal antibody OKT3, phytohemagglutinin, or the combination phytohemagglutinin plus the phorbol ester PMA. Enhanced cyclic AMP generation following mitogenic activation was seen in response to both PGE2 and forskolin, direct activator of the adenylate cyclase, indicating that the amount of adenylate cyclase had increased during the in vitro activation course. In order to investigate whether various T cell subsets in general and in vivo activated T cells in particular would differ in their susceptibility to PGE2, we isolated CD4+, CD8+, CD4-CD8-, CD4+CD45RO+ ("memory"), and CD4+CD45RA+ ("virgin") T cells and studied PGE2-mediated inhibition of CD3-induced proliferation, as well as cyclic AMP generation in response to PGE2, respectively. We found that CD8+ T cells are more susceptible to PGE2 inhibition and produce more cyclic AMP than CD4+ T cells. Double-negative T cells (enriched for gamma delta T cell receptor positive cells) were found to be sensitive to PGE2 as well. Within the CD4+ T cell population, CD45RO+ ("memory") T cells were significantly more sensitive to PGE2-mediated suppression than CD45RA+ ("virgin") T cells. CD45RO+ cells required a 10-fold lower dose of PGE2 for half-maximum suppression of proliferation. However, no difference in cyclic AMP production could be demonstrated between these two subsets. We propose that substantial heterogeneity exists among peripheral blood T lymphocyte subsets regarding their sensitivity to the immunosuppressive action of PGE2 and that the sensitivity of individual cells changes in the course of an immune response.     

Helper activity in antigen-specific antibody production mediated by CD4+ human cytotoxic T cell clones directed against herpes simplex virus

Three HSV type 1 (HSV-1) and HSV type 2 (HSV-2) common ("HSV-type common") and three HSV-1 specific CTL clones, which were CD3+, CD4+, CD8-, 4B4+, and 2H4-, were established. These clones proliferated in response to stimulation with HSV in the presence of autologous APC. The HSV type specificity of the proliferative response was identical with that of the cytotoxic activity of the clones. The cytotoxic activity and the proliferative response were both inhibited by addition of anti-HLA-DR mAb to the culture. After culture of these CTL clones with autologous B cells and macrophages followed by HSV Ag stimulation, anti-HSV antibody was detected in the culture supernatant. The HSV type specificity of the helper function for antibody production was identical with that of the cytotoxicity, i.e., HSV-type common clones, upon stimulation with either HSV-1, or HSV-2, and HSV-1-specific clones, upon stimulation with HSV-1 but not with HSV-2, showed helper activity for anti-HSV antibody production by autologous B cells. Moreover, it was found that these clones produced humoral factors which help autologous B cells to produce antibody. The helper factors were produced by T cell clones in an HSV-type-specific manner. These data suggest that some CD4+ T cells can simultaneously manifest both specific cytotoxicity and helper activity for Ag-specific antibody production by B cells, and that these multifunctional T cells might play an important role in protection against viral infection.     

Cellular receptors for lymphotoxin: correlation of binding and cytotoxicity in sensitive and resistant target cells.

The binding of radioactively labeled lymphotoxin (LT) to both lymphotoxin-sensitive and -resistant cell clones was examined. The sensitive clone had a low- capacity, high-affinity ("specific") binding component, the curve of which closely followed the cytotoxicity curve of the lymphocyte mediator. The capacity of this binding component was calculated to be about 600 molecules of LT/cell. In addition, there was a low-affinity, high-capacity ("nonspecific") binding component. In striking contrast, the high-affinity, low-capacity ("specific") component was absent or greatly diminished from the resistant clone, whereas the low-affinity, high-capacity ("nonspecific") component was present at a similar level as in the sensitive cells.These binding characteristics closely resemble those observed by us and other investigators working with a variety of steroid hormones in steroid-sensitive and- resistant cell lines.     

TRF requirements for in vitro PFC responses to SRBC and R36a. I. TRF is distinct from IL 2 but indistinguishable from polyclonal BCSF

In vitro PFC responses to the thymus-independent (TI) antigen Streptococcus pneumoniae R36a require T cell replacing factor(s) (TRF). This requirement for TRF is as significant as for the thymus-dependent (TD) antigen SRBC. TRF is shown to be distinct from IL 2 by the following observations: 1) culture supernatants from the cloned T cell line L2, collected over an 8-day period after allogeneic stimulation, transiently contain IL 2 activity but maintain high levels of TRF activity throughout 192 hr; 2) L2V, a variant subclone of L2, produces much higher levels of TRF activity than the parental line but no detectable IL 2 activity; 3) the addition of IL2+, TRF- supernatants from the T cell hybridoma FS6-14.13 does not affect the L2V SF-driven PFC responses to R36a or SRBC; and 4) the addition of contaminating T cells to cultures containing T cell-depleted spleen cells, L2V SF, and antigen does not affect the PFC response. TRF does appear to be indistinguishable from polyclonal B cell stimulating factor (BCSF), which stimulates polyclonal PFC responses in the absence of antigen, mitogen, or anti-Ig. The TRF and BCSF activities of L2V SF could not be separated by ion-exchange, hydrophobic-interaction, and gel-filtration chromatography. TRF and BCSF have an apparent m.w. of approximately 40,000.     

Synergy between T cell-replacing factor and bacterial lipopolysaccharides (LPS) in the primary antibody response in vitro: a model for lipopolysaccharide adjuvant action.

Unfractionated spleen cells, B cells from normal mice, and nu/nu spleen cells respond to the addition of bacterial lipopolysaccharide (LPS) and T-cell-replacing factor (TRF) by production of plaque-forming cells (PFC) in excess of the number expected from the addition of LPS and TRF separately. This synergistic activity is dependent on the presence of the antigen, SRBC. Supernatants of both allogeneic spleen cell mixtures and spleen cells cultured with Con A are effective and synergize best at concentrations suboptimal for their ability to act as TRF alone. Culture supernatants of unstimulated normal or fractionated cell populations are ineffective. Synergy is not dependent on the presence of macrophages in the cultures. Purified LPS free from active contaminants, as well as commercially available LPS, show synergy with TRF. Synergy was seen when TRF was added at initiation of culture or 24 hr later. It is suggested that synergy is the equivalent of LPS adjuvant activity, that the role of T cells in LPS adjuvanticity is that of a conventional cooperating cell, and the LPS acts as an adjuvant by inducing B cells to become more sensitive to T cell helper factors.     

Effect of passive administration of alloantiserum containing antibody against putative acceptor(s) for T cell-replacing factor (TRF) in the neonatal stage on development of B cell activity responsive to TRF

Previously, we showed that the antiserum raised in male (DBA/2Ha X BALB/c)F1(DCF1) mice (T cell-replacing factor [TRF]-low response animals) by immunizing them with activated B cells from BALB/c mice (TRF-high-responders) contained antibodies against putative TRF-acceptor site(s). We have now evaluated the hypothesis that neonatal treatment of mice with the above antiserum suppresses the development of B cells responsive to TRF. Male DCF1 mouse anti-BALB/c B-cell antiserum or normal DCF1 mouse serum as a control was injected into BALB/c mice within 24 hr after birth. In the antiserum-treated mice, no augmented primary immunoglobulin M (IgM) antibody responses to sheep red blood cells (SRBC) were observed under the conditions in which markedly augmented IgM anti-SRBC responses were induced in control BALB/c mice, suggesting that development of B cells reacting with male DCF1 mouse anti-BALB/c B-cell antiserum is suppressed by the neonatal treatment with the antiserum. Furthermore, the development of B cell activity responsible for helper factors derived from T cells, such as TRF, was markedly suppressed in the neonatally antiserum-treated mice, whereas activity of B cells capable of interacting directly with helper T cells through antigen-bridges was not significantly affected by the same treatment. Such suppression of the B cell activity could be induced only when the antiserum was administered within 48 hr after birth. Moreover, neonatal treatment of mice with the antiserum induced suppressed responsiveness of B cells to a T-independent type 2 antigen, TNP-Ficoll. Neither serum-borne suppressive serum components nor suppressor cells were detected by the system employed. These results support the hypothesis that TRF responsive B cells constitute a subpopulation distinct from the other B cells capable of cooperating with helper T cells via cognate interaction.     

Inhibition of the in vitro 19S and 7S antibody response by immunoglobulin-binding factor (IBF) from alloantigen-activated T cells

A soluble factor secreted by alloantigen-activated mouse T cells which binds to the Fc fragment of IgG and inhibits complement activation by IgG (immunoglobulin-binding factor, IBF) suppressed the in vitro 19S and 7S antibody response by mouse spleen cells to T-dependent as well as T-independent antigens. IBF inhibited the 19S plaque response best when it was added late during PFC generation (between 48 and 72 hr). On the other hand, when it was left in cultures for up to 60 hr and then removed, antibody synthesis was not inhibited. However, its presence for only 2 hr starting after 72 hr of incubation was sufficient to inhibit PFC formation. The suppressive activity of IFB could be neutralized by adding aggregated mouse IgG prior to the critical stage around 72 hr. These data favour the view that IBF could be a suppressive T cell factor and point to the possibility that IBF may act on already triggered B cells during their final differentiation to active PFC.     

Disparate functional properties of two interleukin 1-responsive Ly-1+2- T cell clones: distinction of T cell growth factor and T cell-replacing factor activities

We describe the properties of two Ly-1+2- T cell clones (Ly-1.14 and Ly-1.21), which are maintained in long-term culture in the absence of other cell types. The clones require media containing a source of interleukin 1 as well as interleukin 2. They retain physiologic responses to interleukin 1, which is required for optimal production of T cell lymphokines by these clones in response to concanavalin A (Con A). The two Ly-1+2- T cell clones differ in their production of lymphokines after stimulation by Con A. The supernatant of clone Ly-1.21 promotes the proliferation of T cells maintained in long-term culture, induces antibody synthesis in cultures of B cells and antigen, and induces the differentiation of cytolytic cells in cultures of thymocytes and antigen; these assays define the properties of T cell growth factor (TCGF), T cell-replacing factor for B cells (TRF-B), and T cell-replacing factor for cytolytic cells (TRF-C), respectively. In contrast, the supernatant of clone Ly-1.14 contains only TCGF activity and does not promote antibody synthesis by B cells or differentiation of cytolytic cells from thymocytes. The results indicates that TCGF and TRF activities reside on independent, although perhaps related, molecules.     

Activation and growth requirements for cytotoxic and noncytotoxic T lymphocytes

The number and nature of the "signals" required for lymphocyte activation have been so repetitively and academically discussed over the last 15 years that both the readers and the authors appear exhausted by such exercises. Yet, what may be considered to be the essential question, the basis for self-nonself discrimination, remains to be clarified. Since it has been established that clonal expansion and maturation to effector functions are brought about by polyclonally ("immunologically nonspecific") active factors, it is obvious that the crucial "step" in this context is the initial interaction of antigen with specific receptors of immunocompetent lymphocytes. This initial discriminatory event appears to proceed differently on the various cell subsets. We first deal with the mechanism of induction and growth of cytotoxic-T-lymphocyte precursors, and then discuss the inductive requirements leading to proliferation of T helper cells.     

Macrophages and T cells control distinct phases of B cell differentiation in the humoral immune response in vitro

The differentiation of B cells in the in vitro PFC-response to red blood cell antigen proceeds through 2 phases. Antigen-reactive B cells acquire the ability to interact with helper T cells in the first phase. This phase is controlled by macrophages through a mediator that they release (Interleukin 1 ([Il-1]). B cells convert into antibody-secreting cells (PFC) in the second phase, which is controlled by helper T cells or by a mediator that they release (T cell-replacing factors [TRF]). This is demonstrated in experiments in which Il-1 increases the number of B cells capable of responding to T cell help. The majority of antigen-reactive B cells reaches that state of differentiation within 40 hr of incubation with Il-1. After this time, the response of B cells depends no longer on the presence of Il-1 but on the presence of T cells or TRF. The presented data suggest that antigen-primed helper T cells (but not unprimed T cells) induce the release of Il-1 by macrophages, thereby also influencing the early phase of B cell differentiation.     

The events of primary T cell activation can be staged by use of Sepharose-bound anti-T3 (64.1) monoclonal antibody and purified interleukin 1

A mitogenic anti-CD3 ("T3") monoclonal antibody (64.1), that stimulates polyclonal T cell activation by a mechanism believed to be similar to antigen via binding to the T cell receptor complex, was utilized in soluble (SOL) and Sepharose-bound (SEPH) forms to dissect the role of accessory cells (AC) and interleukin 1 (IL 1) in supporting T cell activation. The T cell activation pathway was dissected into "early" events including expression of interleukin 2 receptors (IL 2R), increased RNA content, IL 2 release, and "late" (DNA synthesis) events. Unseparated peripheral blood mononuclear cells progressed through all stages of activation when stimulated by either form of 64.1. Stringent AC depletion by plastic adherence, nylon wool adherence, and L-leucine methyl ester (selectively lyses AC) prevented early and late T cell responses to either form of 64.1. The addition of highly purified IL 1 replenished both early and late T cell responses to SEPH-64.1 but not to SOL-64.1. Although SOL-64.1 stimulation of purified T cells induced modulation of the CD3 complex, only SEPH-64.1 induced IL 1 responsiveness, and exogenous IL 1 was then able to support synthesis of RNA, secretion of IL 2, expression of IL 2R, and ultimately, DNA synthesis. Therefore, the stages of early T cell activation owing to stimulation of the CD3-T cell receptor complex and IL 1 responsiveness have been dissected.     

Antibodies to the common leukocyte antigen (T200) inhibit an early phase in the activation of resting human B cells

T191, a monoclonal antibody reactive with the T200 common leukocyte antigen, profoundly inhibits an early event(s) associated with alpha-immunoglobulin M (alpha IgM)/T cell replacing factor (TRF) or alpha IgM/recombinant interleukin 1 and 2 (rIL 1 and rIL 2)-induced tonsillar B cell proliferation. Kinetic analysis of T191-mediated inhibition indicated that the antibody exerts its effect within 12 to 24 hr of the initiation of cultures and rapidly loses its activity thereafter. Small resting B cells are most sensitive to T191 inhibition, whereas B cells with increasing buoyant density (presumably reflecting stages of increased activation) become progressively T191 insensitive. Analysis of RNA synthesis subsequent to alpha IgM crosslinking of surface immunoglobulin demonstrated that T191 reduced [3H]uridine incorporation by up to 38% during the first 20 hr of culture. In contrast to the effects seen with alpha IgM stimulated B cells, T191 had no inhibitory effect upon phorbol myristate acetate-induced B cell proliferation. The inhibitory effect upon B cell proliferation observed with T191 is not unique among other alpha-T200 antibodies. Four of five previously described alpha-T200 monoclonal antibodies had similar inhibitory effects (82 to 57% maximum inhibition of [3H]thymidine incorporation). However, 13.3, an alpha-T200 monoclonal antibody previously shown to block natural killer (NK) cell-mediated killing was without effect. Likewise, those antibodies capable of inhibiting B cell proliferation failed to block NK-mediated cytolysis. Antibody binding experiments together with proliferation inhibition studies suggest that all of the monoclonal antibodies tested recognized distinct epitopes on the T200 antigen. Both observations are of significance because they demonstrate that the effects seen with anti-T200 antibodies represent an interference with highly specific functional regions on the T200 molecules.     

IgG recruiting component (GRC): B cell-derived signal for IgG antibody synthesis.

The B cell-derived soluble factor that has been described as an IgG-recruiting component (GRC) was investigated to: a) ascertain whether it is governed by genetic constraints, b) determine what triggers its synthesis, and c) identify its cellular target. GRC has been shown to be unrestricted by histocompatibility barriers since it enhanced IgG antibody production in mice of diverse genetic backgrounds. Further, we report that eliminating IgG-bearing cells from B cells to be immunized in vitro allows T cells-replacing factor (TRF) to increase the number of IgM but not IgG PFC. Thus, TRF appears to act on IgM-bearing cells by expanding the IgM PFC number. Adding GRC 48 hr after the addition of TRF to such IgG-depleted cells caused expression of IgG PFC. Hence, B cells lacking IgG but possessing IgM surface immunoglobulins appear to be those that are acted upon by GRC. These data indicate that in whole splenic cell populations, GRC is derived from IgG-bearing B cells that are stimulated by antigen and a component in TRF.     

Coexpression of the human HLA-A2 or HLA-B7 heavy chain gene and human beta 2-microglobulin gene in L cells

L cells expressing human HLA-A2 or HLA-B7 class I antigen heavy chains are not recognized by human cytotoxic T lymphocytes directed at HLA-A2 or HLA-B7 antigens. To test whether the absence of human beta 2-m was the cause of the lack of recognition by the human cytotoxic T lymphocytes, coexpression of the human beta 2-m gene and the HLA-A2 or HLA-B7 heavy chain in L cells ("double transfectants") was obtained. In addition, L cells expressing HLA-A2 or HLA-B7 antigens in association with human beta 2-m were obtained by an exchange reaction, in which human beta 2-m from serum replaced the endogenous murine beta 2-m. Both types of transfectant cells were used in 51Cr-release assays and cold target inhibition assays for human cytotoxic T cell clones which were directed at HLA-A2 or HLA-B7. Neither human CTL clones nor a mixture of CTL specific for HLA-A2 and HLA-B7 were able to recognize these cells. Several alternative explanations for these observations are discussed.     

Regulation of T cell cytokine production by dendritic cells generated in vitro from hematopoietic progenitor cells

When dendritic cells (DC) present antigens to T cells, reciprocal cellular interactions occur that lead to cytokine production. This cytokine response is regulated by specific properties of DC, notably their maturation/activation status and perhaps their origin. The latter possibility prompted us to determine if DC produced along distinct developmental pathways induced distinct T cell responses. Hematopoietic progenitor cells with the potential to differentiate into multiple lineages of cells were induced to differentiate into DC along two pathways. One leads to the formation of lymphoid-related DC but not of monocyte-derived DC and is induced by culture of CD34(+) cells with flt-3 ligand (F), c-kit ligand (K), GM-CSF (Gm), IL-1beta ("1"), and IL-7 ("7") (FKGm17). Another pathway with distinct molecular requirements supports in part monocyte-derived DC and is induced by the cytokines F, K, Gm, TNF-alpha (T), and IL-4 ("4") (FKGmT4). DC produced along these two pathways were isolated by flow cytometry and compared. They differed only slightly in phenotype and morphology and both induced Th1-type cytokine production in MLR (mixed lymphocyte reactions). However, on a cell-per-cell basis, FKGm17-DC produced more IL-18 or IL-12 and induced more IFN-gamma by T cells in MLR. Such superior properties were not intrinsically determined by the origin of the DC but were induced by FKGm17 cytokines. We conclude that lymphoid-related DC have the potential to induce Th1 T cell responses but that environmental signals strongly influence T-cell-stimulating properties of DC.