Activation of helper T cells for B lymphocytes in primary mixed lymphocyte cultures

Production of gamma interferon in Mls disparate interactions

The murine T-cell clone E11 isolated from a primary H-2k histocompatible one-way mixed lymphocyte culture of B10.BR anti C3H/Tif spleen cells was used to study multidirectional interactions in strong stimulatory Mls disparate responses. Several parameters have recently been studied, and proliferation of T cells upon stimulation by macrophages or B cells of Mls-disparate stimulator cells, induction of differentiation of B cells of stimulator strains but inhibition of their macrophage differentiation, and the inhibition by E11 T cells of the production of a mitogenic mediator by Mls-disparate spleen cells have been found. As shown in this paper, these phenomena can be explained by an Mlsa, d, e specific induction of gamma-interferon (IFN-gamma) production in the responder B10.BR (Mlsb) E11 T cells. It is suggested that IFN-gamma, as a regulator of feedback mechanisms plays a critical role in Mls disparate T-cell stimulation.

Multidirectional interactions in vitro between lymphoid cells from Mls-disparate strains

Chromosome 1 of the mouse carries a number of genes for alloantigens which can be recognized by T cells, among those the mixed lymphocyte stimulation (Mls) locus and the lymphocyte stimulating determinant (Lsd) locus have been described. The Relationship between the antigens coded for by these two loci has been further analyzed using a B10.BR anti C3H/Tif T cell clone E11. Segregation analysis was done with 167 individuals from backcrosses of (BALB/c (Mlsb, Lsd-) x DBA/2 (Mlsa, Lsd+] F1 animals into BALB/c mice. The analysis of the backcross data and of a limited number of recombinant inbred (RI) strains did not allow the segregated of the two loci, despite the fact that stable clusters were obtained in cluster analysis of the segregation data. The reasons for this failure are discussed. Parallel to the genetic analysis, we have studied the functional properties of the E11 T cell clone. First, there is the proliferation of the E11 T cells upon stimulation by macrophages or B cells of Mls-disparate stimulator strains. Second, there is an induction of differentiation of B cells of stimulator strains, requiring the direct interaction between E11 T and stimulator B cells. Third, there is an inhibitory influence of E11 T cells on the production of a mediator by Mls-disparate spleen cells presumably by their macrophages. We propose that the Mls antigen is a receptor regulating macrophage differentiation and transmitting a signal influencing the production of a mediator. This signal could be either the down regulation of the production of a stimulatory monokine or the induction of the production of an inhibitory monokine. Our presented data demonstrate that the anti Mls response is more complex than hitherto anticipated. It involves a multidirectional interaction between the Mls-disparate cell partners.

Multidirectional interactions in an Mls-disparate response

The murine T cell clone E11, isolated from a primary H-2k-histocompatible, one-way mixed lymphocyte culture of B10.BR anti-C3H/Tif spleen cells, has been used to analyse multidirectional interactions in Mls-disparate responses. Several events can be observed. There is proliferation of T cells upon stimulation by macrophages or B cells of Mls-disparate stimulator cells. In addition, one finds induction of differentiation of B cells of stimulator strains. E11 T cells inhibit spreading and differentiation of macrophages of stimulator strains and also prevent the production of a T cell growth-supporting mediator by Mls-disparate spleen cells. All these phenomena can be explained by Mlsa,d,e-specific induction of gamma-interferon (gamma-IFN) production in the responder B10.BR (Mlsb) E11 T cells. It is suggested that gamma-IFN, as a regulator of feedback mechanisms, plays an essential role in Mls-disparate cell interactions.

The role of immunoglobulin receptors in "cognate" T-B cell collaboration

The functional effects of anti-Ig antibodies have been investigated, using an experimental system where B cell activation is brought about by direct and specific interactions with T helper (Th) cells without participation of surface Ig receptors on the responding B cell. We have used Th cell lines and clones directed to class II major histocompatibility complex antigens of the responding B cells, and titrated into cooperative cultures either purified rabbit anti-mouse mu, or monoclonal mouse anti-delta antibodies. Both types of antibodies greatly enhanced B lymphocyte responses to suboptimal concentrations of functionally efficient Th cells, while they had no effect in cultures containing optimal Th:B cell ratios. In contrast, helper activity by low efficiency Th was, at all Th:B cell ratios, enhanced by appropriate concentrations of anti-Ig antibodies. Anti-Ig effects were exclusively observed when B cells were the targets for "cognate" recognition by Th cells. We conclude that ligand binding to surface Ig receptors on resting B cells fails, in our experimental conditions, to overcome "linked" collaboration, but it greatly facilitates productive Th-B cell interactions. Whatever the mechanisms underlying this facilitation, the observations imply roles of surface Ig in Th-dependent B lymphocyte activation other than either passive "focusing" of antigen or activation into reactivity to soluble, unspecific factors.

Natural effector T lymphocytes in normal mice

The "natural" T-cell activity in normal unimmunized mice was studied. By double-parameter fluorescence-activated cell sorter analysis, it was found that 5-10% of all splenic Lyt-2+ and L3T4+ lymphocytes are large, of which more than half are in mitotic cycle. In contrast with small resting cells of the same phenotype, activated (large) T cells isolated from normal mice are functional effector cells: L3T4+ large cells induce normal B lymphocytes into proliferation and antibody secretion, while large Lyt-2+ cells efficiently suppress B-lymphocyte responses. No effector cell cytolytic activity could be detected among naturally activated T cells. The significance of these findings for the internal activity in the normal immune system is discussed.

T cell-dependent B cell activation

T cell-dependent induction of small, resting B lymphocytes requires direct recognition of antigen and/or I-A/E molecules on the B cell surface by the inducing helper cell, and it does not require the participation of Ig receptors on the responding B cell. Triggering B cell receptors, therefore, are either the I-A/E molecules themselves, or other structures with complementarities on helper cell membranes that become available for productive interactions upon I-A/E recognition. It would appear that signal delivery by such triggering receptors can be regulated by a membrane complex of molecules, involving immunoglobulins, Class II MHC molecules and other classes of receptors, which in selective and distinct manners control the quantitative levels of expression and/or availability of the relevant structures. Classical in vivo observations and our in vitro experiments led us to conclude that induction of B cells does not occur upon binding of T cell-dependent antigens to Ig receptors and, consequently, that B lymphocyte activation by anti-receptor antibodies has no physiological counterpart. Induced B lymphocytes proliferate and mature to high rate secretion of antibodies under the influence of selective growth and maturation factors produced by helper cells which are MHC-unrelated, act polyclonally and have no influence in normal, resting cells. Specific ligand interactions with the membrane molecules participating of that functional complex may also regulate reactivity to either growth or maturation factors, and, thus, control clonal performances and the fate of activated cells.