Partial characterization and purification of murine T cell-replacing factor, TRF. II. Biochemical characteristics

Specificity of antigen induced helper factor for antibody synthesis in vitro and its relation to lymphocytes interaction

Human peripheral blood B-cells can be stimulated with PWM and antigen to produce specific antibody in vitro. This stimulation depends on the presence of T-cells and antigen. T cells, however, can be replaced by a soluble factor derived from a 48-hr culture of T-cells with either PWM and/or antigen. The helper factor, in the absence of antigen, acts as a polyclonal activator causing minimal proliferation of B-cells. When antigen is present, production of specific antibody is not dependent on the source of helper factor. Removal of monocytes abolished synthesis of both Ig and specific antibody although antigen and/or helper factor were present. While production of total IgG required autologous monocytes, the origin of the helper factor was not crucial. Production of specific antibody required that both monocytes and helper factor be derived from the same donor; therefore it seems that cooperation of B-, T-cells and monocytes for production of specific antibody is probably Ia restricted. In contrast, for production of polyclonal Ig (in the absence of antigen), cooperation of B-cells and monocytes with T-cells is not.

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

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

Purification and initial characterization of rat interleukin 2

With the sequential use of dialysis, chromatography on Sephadex G-100, reactive red 120-agarose, p-hydroxymercuribenzoate-agarose, phenyl-Sepharose, poly(L-lysine)-agarose, and isoelectrofocusing, the thymocyte stimulatory factor activity of interleukin 2 from rat spleen was purified about 8,000-fold. By the same procedures, the T cell growth factor activity of interleukin 2 was purified about 6,000-fold. The major peaks of thymocyte stimulatory factor activity and T cell growth factor activity cochromatographed in the various systems used, but T cell growth factor activity without significant thymocyte stimulatory factor activity was sometimes present. Both activities were found to have a pI between pH 5.50 and 6.30. Detectable thymocyte stimulatory factor activity was found at concentrations as low as 0.1-0.2 ng of protein per 0.2 ml. Dose--response plots were linear up to at least 1 ng of protein. Preparations of interleukin 2 labeled with 125I-containing Bolton--Hunter reagent and purified by the procedure mentioned above were electrophoresed on a polyacrylamide gel under denaturing and reducing conditions. The 125I-labeled material migrated in one major band with a molecular weight under 20,000 and three smaller bands with molecular weights of about 20,000, 60,000, and 90,000. Material with thymocyte stimulatory factor activity did not bind to a number of lectin-gels.

Requirement for three signals in "T-independent" (lipopolysaccharide-induced) as well as in T-dependent B cell responses

The requirements for different activation signals in the generation of plaque-forming cell (PFC) responses by positively selected B (surface immunoglobulin-positive) cells were analyzed in low-density cultures to minimize the possible effects of contaminating T cells. Using this system, it is demonstrated that not only in T helper cell (TH)-dependent but also in lipopolysaccharide (LPS)-dependent (i.e., so-called T-independent) PFC responses, the resting B cells have to receive at least three different signals: (a) a major histocompatibility complex (MHC)-specific TH signal that can be bypassed by LPS, (b) an antigen signal, and (c) a second TH signal medicated by MHC- and antigen-unspecific helper factor(s) for B cell responses (BHF) that cannot by bypassed by LPS. Specifically, contact of surface immunoglobulin-positive cells with cloned allo-I-A-specific TH or LPS induced a polyclonal PFC response without significant proliferation, whereas contact with BHF alone (obtained as supernatants from different cloned TH, EL-4 thymoma cells, or secondary mixed leukocyte culture cells) had no effect. Only when LPS, antigen, and BHF, or, alternatively, allo-TH (producing themselves BHF) and antigen were present did clonally expanded PFC responses occur. Thus, the data indicate that both an LPS (or specific TH) signal and an antigen signal are required to render the B cells responsive to BHF. BHF seems to act essentially as a nonspecific growth factor, whereas differentiation into antibody-secreting cells appears to be a preprogrammed consequence of B cell activation by an LPS or specific TH signal.

Culture supernatants of a stimulated T-cell line have helper activity that acts synergistically with interleukin 2 in the response of B cells to antigen

Culture supernatants of an antigen-stimulated long-term alloreactive T cell line, C.C3.11.75, contain a T-cell-replacing factor (TRF) activity for the B-cell response to antigen. These same supernatants show little activity in the T-cell growth assay or the costimulator assay. TRF activity was assayed by using spleen cells that were rigorously depleted of both T cells and macrophages. In this assay preparations containing interleukin 2 and supernatants from stimulated C.C3.11.75 cells are relatively inactive if added alone but show marked synergy when added together. We conclude that the C.C3.11.75 TRF activity is not due to interleukin 1 or to interleukin 2 but to a third factor provisionally designated as (DL)TRF. This activity may be equivalent to the (late-acting) TRF described by Schimpl and Wecker. Evidence is presented suggesting that the helper activity (DL)TRF is a product of the T-cell line.

T cell-dependent activation of resting B cells: requirement for both nonspecific unrestricted and antigen-specific Ia-restricted soluble factors

Cloned murine helper T cells, restricted to the Iab antigens of the major histocompatibility locus and specific for horse erythrocytes as a foreign antigen, produce, in cooperation with antigen and histocompatible adherent cells, soluble factors that replace the helper T cells in their action on B cells. Three types of factors can be distinguished on the basis of molecular weight: proteins having apparent Mr 30,000 (p30) that act antigen- and Ia-nonspecifically as replication- and maturation-inducing factors and proteins having apparent Mr 55,000 (p55) and 125,000 (p125) that act on resting B cells in an Ia-specific, restricted fashion. Neither horse erythrocytes (a T-cell specific antigen) nor p55 and p125, alone or together, stimulate resting B cells to proliferation and maturation. Double occupancy by antigen and p55 or p125, however, renders Ia-compatible, but not Ia-incompatible, resting B cells susceptible to stimulation. The subsequent addition of p30 to these "excited" B cells then results in the proliferation and maturation of clones of horse erythrocyte-specific resting B cells, which then replicate under the stimulatory action of p30. p30 do not bind antigen, nor do they bind anti-Ia or anti-immunoglobulin antibodies. p55 are bound by anti-heavy chain variable region antibodies. p55 are bound by anti-heavy chain variable region antibodies, but not by anti-heavy or anti-light chain constant region antibodies or anti-Ia antibodies. p125 molecules bind horse but not sheep erythrocytes and are bound by anti-heavy chain variable region, but not by anti-heavy or light chain constant region or anti-Ia antibodies. p55 and p125 are likely to be soluble analogues of the antigen-specific, Ia-restricted T-cell receptors of the cloned helper T cells.

Chemical characterization of macrophage cytotoxicity factor, macrophage migration inhibitory factor, T-helper cell-replacing factor and colony-stimulating factor from culture supernatants of concanavalin A-stimulated murine spleen cells

Supernatants from Concanavalin A-stimulated murine spleen cells were subjected to hydrophobic interaction chromatography on phenyl-Sepharose. Macrophage cytotoxicity factor (MCF), macrophage migration inhibitory factor (MIF), T-helper cell-replacing factor (TRF) and colony-stimulating factor (CSF) were bound at high ionic strength and were released stepwise at low ionic strength. CSF thus could be separated from MCF, MIF and TRF and the bulk of other proteins. Chromatograhy of pools containing MCF, MIF and TRF on Sephadex did not lead to a separation of the three activities which were all found in a molecular weight range of 25.000-55.000. Isoelectric focusing of these pools in pH range from 4 to 9 gave two peaks for MCF in a single sharp peak at pH 5.3. The results demonstrate that the four biological activities can be distinguished on a chemical basis and are accessible for purification and chemical characterization.

Direct evidence for a two-signal mechanism of cytotoxic T-lymphocyte activation

The cellular requirements for the activation of cytotoxic T lymphocytes to alloantigens are complex. In addition to cytotoxic precursors (CLPs), metabolically active stimulator cells, adherent accessory (A) cells and antigen-specific helper T cells are also required. However, the requirement for A cells, metabolically active stimulator cells or helper T cells can be replaced by soluble factors or co-stimulator (CoS), a lymphokine obtained by stimulation of murine spleen cells with concanavalin A (Con A). We show here that in the presence of CoS, cultures containing on average one lymph node lymphocyte (LNL) and Con A can be activated to produce single cytotoxic clones. This observation strongly suggests that one of the target cells of CoS is the CLP and provides more direct evidence for a two-signal mechanism for cytotoxic T lymphocyte activation.

[Soluble mediators as a means of communication between lymphozytes in immune reactions (author's transl)]

Soluble mediators play an important role in the positive and negative regulation of immune reactions. This has been particularly well documented for T-B-cooperation in the humoral immune response to T-dependent antigens. T-helper cells produce a T-cell replacing Factor (TRF) upon mitogenic or antigenic stimulation. It provides the signal to antigen triggered B-cells to begin with active antibody synthesis and secretion and thus it is a positively regulating mediator. Additional functional and some structural characteristics of TRF are described. Antigen specific and non-specific suppressor factors seem to be involved in the negative regulation of immune responses. Thus, the communication between cells of the immune system is largely conducted via soluble signal substances.

T cell-produced immunoglobulin binding factor (IBF) bears determinants coded for by the I region of the major histocompatibility complex and lacks allogeneic restriction

An immunoglobulin binding factor (IBF) produced by in vivo alloantigen-activated T cells suppresses in vitro antibody production to sheep red blood cells (SRBC) and probably represents the soluble form of the T cell Fc receptor. To study the relationship between IBF and the major histocompatibility complex (MHC), two types of experiments were undertaken. First, different IBF were prepared by injecting thymocytes from mice of H-2k, H-2b and H-2d haplotypes into irradiated, allogeneic recipient mice. Cells recovered in the spleens five days later were incubated for 2 h at 37 degrees C, and IBF was purified by affinity chromatography on insolubilized IgG. Purified IBF was then applied to immunosorbents prepared with anti-H-2 and anti-Ia anti sera. Acid eluates were then tested for their suppressive activity on in vitro antibody production to SRBC. Under these conditions, IBF was found to react with antisera raised against products of the whole MHC and of the I region of the MHC, but not with anti-H-2 D antisera. These data indicate that IBF bears, or is associated with Ia determinants. Second, IBF preparations from mice of H-2k, H-2b, H-2d haplotypes were tested for their capacity to suppress the in vitro antibody production to SRBC by spleen cells of a series of mouse strains. The data indicate that IBF is not genetically restricted in its function.

Cell-mediated immunity to antigens associated with murine sarcoma virus-induced tumors: augmentation of cytolytic T lymphocyte activity by successive specific and nonspecific stimulation in vitro

It has been shown previously that lymphoid cells from mice which have rejected a tumor induced by the Moloney sarcoma virus-leukemia virus (MSV-MLV) complex develop high levels of specific H-2-restricted cytolytic T lymphocyte (CTL) activity after in vitro stimulation with syngeneic, irradiated MLV-induced lymphoma cells in mixed leukocyte-tumor cell cultures (MLTC). Attempts to further increase lytic activity by restimulating long-term MLTC cells with syngeneic, irradiated lymphoma cells have met but with limited success. This report shows that, in contrast to the lack of increased activity observed after specific stimulation with lymphoma cells, nonspecific stimulation of long-term MLTC cells either with supernatants from secondary mixed leukocyte cultures (2 degrees MLC SN) or with supernatants from concanavalin A-stimulated spleen cells leads, on a per cell basis, to a further 5 to 10-fold increase in CTL activity. The stimulatory activity of 2 degrees MLC SN is due to a factor(s) of apparent mol. wt. of 25,000 to 40,000. The activity of the CTL populations formed under these conditions is at least 100-fold higher against syngeneic as compared to allogeneic MLV-induced or unrelated tumor cells.