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Biomedical subjects

A Coutinho

Publications and source records attributed to A Coutinho.

At least 289 records · Page 16Linked to original sources
PubMed1980

Specific T helper cells that activate B cells polyclonally. In vitro enrichment and cooperative function.

C3H/HeJ T cells which specifically recognize B cell-surface antigens of the related, major histocompatibility complex-compatible C3H/Tif strain, can be substantially enriched in vitro by long-term exposure (2--6 wk) of primed lymph node cells to the relevant cellular antigens. These enriched T cells contain functional helper cells as demonstrated by their capacity to induce large numbers of Ig-secreting plaque-forming cells (PFC) in cultures of antigenic B cells. The cooperative interaction results in activation of a large fraction of all splenic B cells, with consequent exponential growth and maturation to high rate secretion of IgM, IgG1, and IgG2, but not IgG3. The IgM PFC response includes antibody specificities to a number of different antigens and can be considered, therefore, as polyclonal. The T helper cell-dependent B-cell response is insensitive to inhibition by anti-delta antibodies, and in contrast with lipopolysaccharide-induced PFC responses, is only partially sensitive to the inhibitory effects of anti-mu antibodies. Finally, B-cell activation to growth and maturation by helper T cells strictly required direct T-cell recognition of antigens on the surface of responding B cells, leading us to the conclusions that if any soluble factors are generated in the collaborative process, they are either antigen specific or incompetent to initiate B-cell growth.

Animals↗
PubMed1980

Two distinct factors are required for induction of T-cell growth.

The molecular and cellular basis of T-lymphocyte activation remains a central question in immunology. The growth of already proliferating T cells is known to depend on T-cell growth factor (TCGF), a physiological mitogen. Noncycling T lymphocytes, however, are not sensitive to TCGF. They require a short contact with mitogenic lectins, such as concanavalin A (Con A) or leukoagglutinin to bind and respond to TCGF, and will thereafter maintain exponential growth for long periods provided that TCGF is not limiting. While the induction of TCGF reactivity results from the direct contact of Con A with resting T cells, the lectin-dependent production of TCGF is known to involve two cell types, both present in mouse spleen. One consists of I-A-negative cells, most of which are Thy-1-positive T lymphocytes, and the other consists of I-A-positive, immunoglobulin-negative, Thy-1-negative cells, most of which are macrophages. The nature of the respective contributions of the two cell types, and in particular the cellular origin of TCGF, has not yet been established. We have now established the I-A-negative population as the source of TCGF and show here that macrophages are required to supply a 20,000-molecular weight factor, chemically and functionally distinct from TCGF, which supports the production of TCGF by the I-A-negative cells.

Animals↗
PubMed1980

Major histocompatibility complex-restricted and unrestricted T helper cells recognizing minor histocompatibility antigens of B cell surfaces.

The present experiments analyze the functional properties of helper T cells specific for "minor" histocompatibility antigens. T cells from C3H/HeJ mice, primed in vivo and highly enriched in vitro for reactivity to membrane antigens of C3H/Tif B cells, specifically proliferate, and provide polyclonal help to splenic B cells from strains carving a variety of different H-2 haplotypes on C3H or BALB backgrounds, while failing to respond to cells carrying the same H-2 haplotypes on C57BL or A backgrounds. Since it has been previously demonstrated (A.A. Augustin and A. Coutinho, J. Exp. Med. 1980. 151: 587) and B cell activation in this system strictly requires direct, specific recognition of B cell surface antigens by helper cells and does not result from the production of soluble "mitogenic" or "nonspecific helper factors", it is concluded that this phenomenon represents specific, major histocompatibility complex (MHC)-unrestricted T cell help. In addition, it has now been found that expression of helper activity requires viability of the helper cells and is partially radiation-sensitive. Lack of MHC restriction is not a general property of specific helper cells which directly recognize B cell "minor" antigens, since BALB.C3H anti-C3H/Tif T cells appear to be restricted by H-2 in their polyclonal helper activity. The helper activity mediated by specific anti-"minor", H-2 restricted helper cells could not be inhibited by anti-VH antibodies, and the inhibition obtained with anti-Ia antibodies appeared to operate at the level of B cell induction, rather than at the level of helper cell activation.

Animals↗
PubMed1980

Immunoglobulin C-gene expression. I. The commitment to IgG subclass of secretory cells is determined by the quality of the nonspecific stimuli.

Polyclonal stimulation of normal splenic B lymphocytes with either lipopolysaccharide (LPS) or helper T lymphocytes specific for B cell surface antigens results in the selective expression of IgG subclasses by the secretory cells: in addition to IgM-secreting plaque-forming cells (PFC), thymus-independent stimulation leads to the development of IgG2 and IgG3 PFC, while helper cell-dependent activation leads to IgG1 and IgG2 PFC. This cannot be solely explained by selective stimulation of distinct B cell subpopulations, because purified LPS-reactive blasts if restimulated by helper cells switch to IgG1 while if maintained with LPS switch to IgG3. The simultaneous stimulation of splenic B cells with LPS and helper cells results in additive IgM and IgG2 responses, but in the selective suppression of IgG3 PFC with a concomitant synergic enhancement of IgG1 responses. These results are interpreted to indicate that the expression of IgG C genes in proliferating B lymphocytes is directed by the quality of nonspecific stimuli.

Animals↗
PubMed1980

IgM antibodies induce the production of antibodies of the same specificity.

Injection in normal mice of IgM antibodies against sheep erythrocytes or dextran, in the form of an immune serum depleted og IgG, induces direct plaque-forming cells of the same specificity as the injected antibodies. The response is 10--70 times higher than the background plaque-forming cell titer of untreated control mice. Nanogram amounts of IgM induce a detectable response, and a ceiling is reached with a few hundred nanograms of monoclonal IgM. The inducing agent is not residual antigen: (i) treatment of the injected material and the recipients with dextranase abolishes the immunogenicity of dextran, but not the response to anti-dextran IgM; (ii) monoclonal IgM specific for sheep erythrocytes or trinitrophenyl likewise induces plaque-forming cells of the respective specificity, but variant hybridoma products (in which the light chain is that of the myeloma parent) are inactive. In normal mice, IgM-induced antibody responses were observed with antibodies to both thymus-dependent and thymus-independent antigens, but such could not be induced in athymic (nude) mice. Because the mechanism underlying this phenomenon would operate also in a normal immune response and, presumably, in the normal dynamic state of the immune system of unstimulated animals, a network regulation among the elements of the immune system itself is implied.

Animals↗
PubMed1979

Mitogen-activated B-cell blasts reactive to more than one mitogen.

One of three splenic B cells of 2- to 3-mo-old C57BL/6J or C3H/Tif mice are activated either by lipopolysaccharide (LPS) or by lipoprotein (LP) to grow and to mature to IgM-secreting cells. When mitogen-activated blast cells, after a 2-d activation period, are separated from nonactivated, small cells by velocity sedimentation, and no mitogen is readded, the blasts do not continue to grow but do continue to secrete IgM for several days. When the homologous mitogen is added for restimulation, the blast cells continue for several days to divide every 18 h and to develop IgM-secreting, plaque-forming cells. Frequency analyses at limiting dilutions of reactive B-blasts show that one cell in approximately equal to 1.2--1.5 blasts continue to grow and mature in the presence of the homologous mitogen, either LPS or LP. When the B-cell blasts obtained in a first activation period with either LPS or LP are restimulated with a heterologous mitogen, LPS, LP, Nocardia mitogen or mitogens contained in fetal calf serum a high proportion of the blasts continue to grow and mature to IgM-secreting cells. Frequency analyses show for LPS- or LP-blasts, restimulated in a heterologous fashion with either LP or LPS, that one cell in 1.35--1.5 blasts continue to divide and to mature to IgM-secreting cells. C3H/HeJ-splenic B-cells, which are LPS nonresponders, can only be activated to blast cells by LP. These LP-activated blasts can be restimulated by the homologous LP and by Nocardia mitogen and mitogens of fetal calf serum, but not by LPS. The results indicate that the majority of splenic B cells of 2- to 3-mo-old C57BL/6J or C3H/Tif mice are reactive to more than one B-cell mitogen. B cells, therefore, can possess in their surface membrane multireactive mitogen-receptor complexes which regulate growth and maturation.

Animals↗
PubMed1979

Studies on T lymphocyte activation. I. Requirements for the mitogen-dependent production of T cell growth factors.

Conditioned media (CM) obtained from concanavalin A (Con A)-stimulated spleen cell cultures maintain mitogen-derived T cell blasts in exponential growth for indefinite periods of time. Such purified T cell blasts do not respond to Con A, and the growth-promoting activity in CM is independent of the mitogenic lectin used for its production. However, the appearance of activity in CM is Con A dose-dependent. Furthermore, the production of these T cell growth factors is independent of B cells, while it requires both T cells and nontheta-bearing, probably Ia-positive cells present in normal and nude spleens. On the other hand, the T cell blasts which are reactive to the growth factors, neither produce CM by themselves nor can they cooperate with nude spleen cells for its production, in the presence of a mitogenic lectin. Since the concentration of growth factors in CM determines the extent of T cell growth, we propose that the growth of some T cells is necessarily dependent upon the activity in CM described here and, consequently, that the basis for T cell activation is the induction of such growth factors.

Animals↗
PubMed1979

Studies on T lymphocyte activation II. The target cells for concanavalin A-induced growth factors.

Growth factors contained in Con A(concanavalin A)-conditioned media (CM) maintain exponential growth in T cell blasts derived from mitogen stimulation of spleen cells with Con A, phytohemagglutinin, lentil lectin and pokeweed mitogen (PWM), as well as from mixed lymphocyte reactions to H-2D or I-C-encoded determinants and from non-H-2 Mls locus-controlled reactions. Such growth factors are strictly T cell blast-specific, inasmuch as they do not stimulate resting, small T or B lymphocytes nor B cell blasts generated by lipopolysaccharide or lipoprotein activation. The responsiveness of T cell blasts to CM appears to be the result of the availability on the cell surface of an acceptor site for growth factors which is not expressed in resting cells, because T cell blasts, but not small spleen cells, absorb out the growth-promoting activity contained in CM. Furthermore, lectins such as Con A and PWM interfere with the blast surface membrane in such a way that they inhibit the response to growth factors. Finally, there is no detectable allotypic or isotypic restriction in the activity of Con A-CM on a variety of target T cell blasts.

Animals↗
PubMed1979

Wheat germ agglutinin activates macrophages for collaboration with B cells.

Wheat germ agglutinin (WGA), added to Mishell-Dutton-type cultures of nude spleen cells challenged with erythrocyte antigens, allows a primary specific plaque-forming cell (PFC) response. WGA, however, does not display direct mitogenicity to either T or B lymphocytes. The activity of WGA in the specific PFC response is macrophage-dependent and parallels a nonspecific PFC response in the same cultures.

Animals↗