Biomedical subjects

M Brunswick

Publications and source records attributed to M Brunswick.

27 records · Page 2Linked to original sources

PubMed1989

Surface immunoglobulin-mediated B-cell activation in the absence of detectable elevations in intracellular ionized calcium: a model for T-cell-independent B-cell activation.

We recently showed that anti-immunoglobulin conjugated to high molecular weight dextran is 1000-fold more mitogenic for B cells than unconjugated anti-immunoglobulin. This system serves as a model for T-cell-independent type 2 antigens such as haptenated Ficoll, dextran, and bacterial polysaccharides, which can also stimulate B-cell proliferation and antibody production at low concentrations. We show here that conjugated anti-immunoglobulin, at concentrations that stimulate significant increases in expression of major histocompatibility complex class II molecules and incorporation of thymidine into DNA, does not induce detectable modulation of surface immunoglobulin. These results indicate that the facilitated T-cell-independent B-cell activation by polysaccharide antigens may result from inability to modulate surface immunoglobulin, possibly resulting in persistent and/or repetitive signaling. Early large increases in Ca2+ and breakdown of inositol phospholipids presently thought to be involved in transduction of the mitogenic signal are not detectable at low concentrations of conjugated anti-immunoglobulin, raising the possibility that these biochemical events may not in fact be central to this signaling pathway.

Animals↗

PubMed1988

Picogram quantities of anti-Ig antibodies coupled to dextran induce B cell proliferation.

To investigate the properties which enable type 2 Ag, as exemplified by dextran and Ficoll, to stimulate high levels of antibody responses in the relative absence of T cells, we conjugated anti-IgD and anti-IgM mAb to both dextran and Ficoll and examined their B cell-activating properties. Such conjugated anti-Ig antibodies stimulated both early and later stages of B cell activation at picogram concentrations, which are at least 1000-fold lower than that required for B cell stimulation by unconjugated anti-Ig antibodies, and the level of proliferation they stimulated was on average 10-fold greater. Furthermore, concentrations of anti-Ig dextran (100 pg/ml) which modulated little sIgD from the B cell surface were strong inducers of enhanced B cell expression of MHC class II molecules. Conjugation of Fab fragments of anti-IgD or nonmitogenic anti-IgM mAb to dextran rendered them as mitogenic as dextran conjugated to strongly stimulatory anti-IgD or anti-IgM antibodies. The ability of dextran and Ficoll to serve as effective carrier molecules for anti-IgD was not related solely to their large m.w., because anti-IgD coupled to polymerized BSA (m.w. 1.5 X 10(6), was only 10- to 50-fold more potent than unconjugated anti-IgD antibodies at stimulating B cell DNA synthesis. These results suggest, therefore, that the unique ability of picogram concentrations of haptenated type 2 Ag to stimulate Ig secretion in the absence of T cells may be a function of their ability to promote effective cross-linking without resulting in the modulation of sIg. This would enable such Ag to mediate repetitive B cell signaling, a situation that cannot be achieved by unconjugated anti-Ig antibodies which result in modulation of sIg at their mitogenic concentrations. These compounds therefore may be employed to study B cell activation stimulated by sIg cross-linking at concentrations that may more closely reflect those which are achieved under physiologic conditions by type 2 Ag.

Animals↗

PubMed1987

A role for IFN-gamma and NK cells in immune responses to T cell-regulated antigens types 1 and 2.

Responses to antigens that have been previously recognized as T cell-independent are now known to be dependent on some form of T-cell (or T cell-derived) help. This T-cell dependency, however, can be most easily noted when responses to small resting B cells are examined, since responses of larger, size-separated B cells to TNP-Ficoll require little if any T-cell help. The type of ancillary "help" that is required for the responses to type 1 and type 2 antigens exhibits certain similarities as well as differences. Thus, responses to both of these antigens can be stimulated in the presence of L3T4- or L3T4+ cells as well as in the presence of IL2. However, while the presence of IFN-gamma may be significantly inhibitory for the responses to the type 2 antigen TNP-Ficoll, they do not appear to influence the response to the type 1 antigen TNP-BA. Furthermore, while vigorous elimination of NK cell activity from purified B-cell populations enhances the response to TNP-Ficoll, it has no discernible effect on the response to TNP-BA. These results suggest that determination of type 1 and type 2 antigens may be made not only based on the characteristics of the carrier molecule but also on the nature of ancillary help that needs to be provided for these antigens to stimulate optimal responses. Type 1 antigens have polyclonal B-cell activating properties and stimulate responses which are not influenced by IFN-gamma, type 2 antigens have no polyclonal B-cell activating properties and stimulate responses which can be influenced by IFN-gamma.

Animals↗

PubMed1986

Functional interactions of human and murine lymphoid cells. I. Analysis of primary and secondary responses.

In this study human T-cell responses against murine alloantigens were analyzed. The results show that optimal primary responses are obtained from peripheral blood mononuclear cells only when murine splenic adherent cells (SAC) were used as antigen. Further analysis revealed that human T cells were able to respond directly to murine cells without the need for antigen reprocessing; however, human interleukin 1 (IL-1) was required for optimal stimulation. In contrast, secondary proliferative responses to murine cellular antigens could be induced from primed T cells even in the absence of SAC and/or IL-1. These proliferative responses, and in addition, cytotoxic T-cell responses, were specific for the priming antigen. Long-term human T-cell lines specific for murine alloantigens were found to replace the need for murine T cells in antigen-specific murine B-cell responses to sheep red blood cells. The mechanism of help delivered by the human T cells appeared to be by the release of nonspecific helper-T-cell factors. The evidence presented for this is the inability of these cells to stimulate cells from mice that express the X chromosome B-cell defect xid.

Animals↗

PubMed1986

T-cell replacing factor activity of recombinant-derived interleukin-2 requires gamma-interferon.

In this study we show that recombinant-derived human interleukin-2 (rIL-2) has potent T-cell replacing activity in antigen-driven murine antibody responses of T-depleted spleen cells. This T-cell replacing factor (TRF) effect of rIL-2 is antigen specific. By the use of a variety of antibodies to gamma-interferon (IFN-gamma), including antibody from an interspecies hybridoma, we demonstrate that this TRF activity depends upon the production of IFN-gamma in the responding cell cultures, i.e., antibody to IFN-gamma blocks TRF activity. In addition, we show that the cell-to-cell allogeneic helper effect of T cells for antibody responses is similarly inhibited by antibodies to IFN-gamma. The inhibition of response produced by the antibodies is reversed by the addition of excess rIFN-gamma to the cultures. The results demonstrate that IFN-gamma is a necessary intermediate mediator for TRF activity mediated by IL-2 and also by T-cell-mediated help for B cells. Thus, even recombinant-derived lymphokines have complex secondary levels of action on responding cells. Antibodies to individual lymphokines are clearly a powerful resource to analyze the role of soluble factors in cellular responses.

Animals↗

PubMed1985

Obligatory role of gamma interferon in T cell-replacing factor-dependent, antigen-specific murine B cell responses.

The role of gamma interferon (IFN-gamma) in T cell-replacing factor (TRF) activity for antigen-specific plaque-forming cell (PFC) responses in vitro was studied using antibodies to murine IFN-gamma (Mu IFN-gamma). TRF activity was present in supernatants (Sn) of Con A- or mixed leukocyte reaction-stimulated murine spleen cells as well as in an IL-2-rich fraction of phytohemagglutinin-stimulated human peripheral blood lymphocyte Sn and in the Sn of the Gibbon T lymphoma MLA-144. The human TRF was highly active with cells from nu/nu mice and normal mice but not with cells from animals with the xid immunologic defect, similar to the activity of murine TRF. Antibodies to IFN-gamma consisted of hyper-immune rabbit antisera, IFN-gamma affinity-purified rabbit immunoglobulin and an interspecies hybridoma specific for Mu IFN-gamma. The results show that the activities of all preparations of TRF are markedly diminished or abrogated by antibody to Mu IFN-gamma but not by antibodies to human IFN-gamma (Hu IFN-gamma), nor by normal rabbit sera or purified rabbit Ig. The degree of inhibition was dose dependent and was quantitatively reversed by the addition to the cultures of recombinant-derived Mu IFN-gamma (Mu rIFN-gamma) but not Hu rIFN-gamma. This reversal was fully antigen specific and thus not attributable to polyclonal B cell activation by IFN-gamma, which is inactive alone in the TRF assay. Kinetic analysis shows that IFN-gamma must act by 24-48 h to produce PFC responses at 4 d. Together, the data demonstrate that IFN-gamma is a necessary mediator for TRF effects and that IFN-gamma is induced by TRF from T-depleted murine spleen cells in sufficient quantity to support large antibody responses. The source of this IFN-gamma may be the potent natural killer cells that are induced in cultures stimulated with TRF.

Animals↗

PubMed1982

Viral antigens act as helper determinants for antibody responses to cell surface antigens.

Thy-1 alloantigens on murine thymus cells are weak immunogens in vivo for PFC responses in the absence of other antigenic disparities between the donor and recipient. Our previous work showed that non-H-2 alloantigens acted as helper determinants to augment anti-Thy-1 PFC responses. In this report we demonstrate that strong helper antigens are also produced by infection of donor thymus cells with viruses such as HSV-1, NDV, or vaccinia. This helper effect (as much as 30-fold) for a cellular antigen, requires linked recognition (expression of Thy-1 and virus in the same cell membrane), is T-dependent, antigen- (virus) specific, and is Thy-1-specific. The recognition of the viral helper sites is not restricted by the MHC genotype of the thymus cell donor, indicating that host reprocessing of antigen occurs. These are the first results that show that adventitious antigens may function as helper determinants for antibody responses to native membrane antigens and may be the mechanism that initiates several forms of acute post-viral autoimmune disease.

Animals↗

PubMed1982

I-J restriction of T cells that suppress in vivo antibody responses to Thy-1.

The contact-sensitizing haptens dinitrophenyl (DNP) and oxazalone (Ox) act as helper determinants for antibody responses to Thy-1 when conjugated to donor thymus cells. The helper effect is transferrable from primed to naive mice with spleen cells, producing specific augmentation of in vivo PFC responses to Thy-1. The helper cells are hapten-specific and require associative recognition of hapten and Thy-1, excluding a role for nonspecific B cell activation. The phenotype of the helper cells is Thy-1+ and Lyt-1+2-. Antigen-specific suppression could be readily generated by using an inoculum of DNP-modified syngeneic RBC. T cells from these suppressed donors (Ts) were shown to abolish the helper effects of TH in adoptive transfer experiments in vivo. These Ts were characterized as Thy-1+ and Lyt-1-2+. A requirement for MHC compatibility at the I-J subregion was necessary between the Ts and the recipient to obtain a transfer of suppression.

Animals↗

PubMedDate not supplied

The isolated major histocompatibility complex class I alpha3 domain binds beta2m and CD8alphaalpha dimers.

The MHC class I molecule plays a crucial role in cytotoxic lymphocyte function. The heavy chain of the MHC class I molecule can form many non-covalent interactions with other molecules on multiple domains and surfaces. We have generated an isolated alpha3 domain of a murine MHC class I molecule and evaluated the contribution of this domain to binding with the MHC class I light chain, beta2m, and CD8. The alpha3 domain binds beta2m at a thousand-fold higher concentration than the whole MHC, and binds CD8alphaalpha with a dependence on the alpha3 CD loop. Our results are relevant for models of MHC folding and CD8-MHC function. The study of individual domains of complex molecules is an important strategy for understanding their dynamic structure and function.

Binding Sites↗