Biomedical subjects

M K Hoffmann

Publications and source records attributed to M K Hoffmann.

At least 37 records · Page 2Linked to original sources

PubMed1996

The superantigen Staphylococcus enterotoxin B induces a strong and accelerated secondary T-cell response rather than anergy.

The primary and secondary immune response of V beta 8+ T cells to the bacterial superantigen Staphylococcus enterotoxin B was compared in BALB/c mice. Secondary responder T cells were found to up-regulate the expression of the adhesion molecule LFA-1 faster, and to enter the cell cycle earlier than primary responder T cells. Both, primary and secondary responder T cells upregulate the expression of CD2 and CD25 and turn into blast cells with superimposable time kinetics. Secondary responder T cells terminate DNA synthesis, blast formation and the upregulation of CD25 and CD2 expression earlier than primary responder T cells and become more rapidly deleted. Two days after superantigen challenge, when primary responder T cells reach peak activity in terms of DNA synthesis and blast formation, secondary responder T cells have returned to the size of microblasts and ceased to replicate their DNA. Whereas our results are consistent with the observations leading to the concept of superantigen-induced T-cell anergy, they demonstrate, by revealing the accelerated vigorous secondary T-cell response to the superantigen, that this concept requires reconsideration.

Animals↗

PubMed1995

T cell antigen receptor engagement abrogates CD4-mediated T cell deletion in vivo.

We have previously shown that the engagement of CD4 by specific antibody in the mouse initiates a T cell apoptosis response with the following features: spleen and lymph node CD4+ T cells migrate into the bloodstream within minutes of anti-CD4 administration where they exhibit the phenotype of null cells. If they are capable of expressing functional Fas protein on their surface they degrade their DNA and disintegrate rapidly. We show here that the engagement of the T cell antigen receptor blocks the CD4-mediated deletion process in mouse. Anti-CD4-reactive T cells avoid the exodus into the bloodstream when their TCR is engaged by anti-CD3 or by a superantigen, do not modulate surface receptors and are not deleted. In contrast to the apoptosis-inducing CD4-specific antibody which causes migration of lymphocytes from lymphoid organs into the blood stream, the T cell-activating CD3-specific antibody causes lymphoid cell redistribution in the opposite direction, from the bloodstream to lymphoid organs. The TCR-mediated protection of T cells against CD4-mediated deletion lasts for several hours but ceases before the T cells become blasts.

Animals↗

PubMed1994

CD4 engagement induces Fas antigen-dependent apoptosis of T cells in vivo.

CD4 is a T lymphocyte receptor for major histocompatibility complex class II antigens. It is referred to as coreceptor because it synergizes with the T cell receptor for antigen when both receptors become engaged simultaneously. We show here in mice that when engaged by antibody independently of the T cell antigen receptor, CD4 induces T cells to undergo apoptosis. Several features of this process were identified. The expression of an intact Fas protein is a requirement for CD4-mediated T cell death. Mice homozygous for the lpr mutation which are defective in the expression of Fas and in their ability to delete lymphocytes apoptotically fail to delete anti-CD4-reactive T cells. Sessile anti-CD4-reactive T cells leave their homing environment in lymphoid organs and modulate their cell surface molecules, e.g. CD2, CD3, CD4. A massive influx of lymphoid cells with null-cell phenotype occurs in the blood where they begin to reexpress cell surface markers. With their arrival in the circulation, anti-CD4-reactive T cells develop features of DNA degradation typical of apoptosis. More than one third of the circulating lymphoid cells show apoptotic features 7-8 h after anti-CD4 injection. Their frequency declines subsequently presumably due to their physical disintegration via shedding of apoptotic bodies and phagocytosis. Our data show that when not obliged to the activation process by the antigen receptor, CD4 can mediate deletion signals. Thus, besides functioning as coreceptor with the antigen receptor, CD4 has a function of its own in facilitating the induction of apoptosis.

Animals↗

PubMed1994

Deletion of T lymphocytes in human CD4 transgenic mice induced by HIV-gp120 and gp120-specific antibodies from AIDS patients.

CD4, a T cell receptor for major histocompatibility complex class II antigen, is a key regulator of immunological reactivities. When engaged together with the T cell antigen receptor, CD4 enhances immune reactions, whereas when ligated independently of the antigen receptor CD4 inhibits the activation of T cells or initiates their deletion. CD4 serves also as a receptor for the human immunodeficiency virus (HIV), which binds the receptor with high avidity through its envelope molecule, gp120. Studies in tissue culture have shown that its affinity to CD4 gives the virus opportunities to utilize CD4-mediated signaling and to manipulate immunocytes. We show here in human CD4 transgenic mice that appropriately cross-linked HIV envelope protein causes massive deletion of HIV-reactive T cells in vivo.

Animals↗

PubMed1994

Activation of human T cells by the superantigen Staphylococcus enterotoxin B: analysis on a cellular level.

Superantigens interact with and activate a sizeable fraction of T cells characterized by expression of specific V beta gene segments of their antigen receptor. The massive activation of T cells in an organism is considered responsible for clinical symptoms associated with superantigen-producing bacteria. Here we studied the in vitro activation of human T cells by the superantigen Staphylococcus Enterotoxin B on a cell by cell basis. Superantigen-reactive T cells were stained with a V beta 12-specific monoclonal antibody and analyzed in a cytofluorograph. Blast formation of SEB-reactive T cells occurs within 12 h and reaches a plateau after 24 h. Double-staining of V beta 12+ T cells with antibodies against different T cell activation or adhesion surface molecules revealed a time-dependent differential upregulation for CD2, CD11 = LFA-1, CD25, CD28, CD69, and HLA-DR. The expression of CD3, CD4 and CD5 was not influenced by the superantigen. The rapid phenotypic changes of superantigen reactive T cells in terms of marker expression and cell size could provide early tools in diagnosing diseases caused by superantigens.

Antigens, CD↗

PubMed1993

Anti-histone autoantibodies react specifically with the B cell surface.

In an attempt to induce an immune response against Mls-1a antigens by immunizing C57B1/6 mouse (Mls-1b) with purified B cells from DBA/2 mouse (Mls-1a), we generated a panel of monoclonal antibodies from which the 5B9.6 mAb, taken as a representative antibody, was thoroughly investigated. This antibody specifically reacts with B cells from all mouse strains studied including C57Bl/6 mice as shown by FACS analysis of double-antibody labelled spleen cells. Using enzyme immunoassays and immunoprecipitation techniques, 5B9.6 mAb was found to be specific for histones. Amino acid sequence analysis of a peptide derived from a 5B9.6-immunoprecipitated polypeptide from DBA/2 B cells showed a 100% homology with a sequence within H2B histones. Furthermore, 5B9.6 mAb was able to interact with the cell surface of 7OZ/3 cell line, known as a typical pre-B cell line. The presence of histones can be modulated on the surface of 7OZ/3 cells since this antigen was upregulated after exposure of these cells to a cocktail of IL-1 and cAMP. Finally, 5B9.6 mAb was shown to interact with freshly isolated B cells from human peripheral blood.

Amino Acid Sequence↗

PubMed1993

Differential expression of T cell receptor variable beta genes on CD4+ and CD8+ T cells: influence by sex linked genes?

We examined the expression of seven V alpha or V beta T cell receptor (TCR) segments on human CD4+ and CD8+ T cells. Confirming previously published results, we found a preferential expression of four V segment gene products on CD4+ T cells. One of these markers (V beta 6.7) was constantly expressed on more CD4+ T cells than CD8+ T cells. None of the analyzed blood samples showed a complete deletion of T cells expressing a particular V beta gene segment. In addition, our data provide the first evidence that genes on sex chromosomes may influence the formation of the human T cell repertoire. The ratio of CD4+/CD8+ T cells expressing V beta 12 gene products was always > or = 1 in female donors, whereas approximately 30% male donors exhibited more CD8+V beta 12+ T cells than CD4+V beta 12+ T cells.

Adult↗

PubMed1993

Characterization of anergy to the superantigen Staphylococcus enterotoxin B.

In vivo administration of superantigens leads to activation and subsequent depletion or anergy of T cells expressing defined V beta-T cell receptors (TCR). Superantigens have therefore become intensively studied tools for examining parameters of immunoregulation and they may represent model antigens for pathogenic agents. An HIV-encoded superantigen has for example been implicated in the dramatic loss of helper T cells in AIDS. We investigated the response of V beta 8+ T cells in mice after primary and secondary exposure to the superantigen Staphylococcus Enterotoxin B (SEB).

Animals↗

PubMed1992

A stimulatory Mls-1 superantigen is destroyed by ultraviolet light while other Mtv-7 antigens remain intact. Significance for Mls-1 unresponsiveness.

Accessory cells present Ag together with costimulatory signals as immunogens and without costimulatory signals as tolerogens. Responsiveness and unresponsiveness are thus alternatives of T cell immune reactions to Ag. Superantigens appear to make an exception; being presented by accessory cells capable of providing costimulatory signals, these Ag induce a strong T cell response but leave T cells unresponsive to a secondary challenge (anergy). We show here that T cell anergy is not a mandatory consequence of superantigen-induced activation. Mls-1- BALB/c recipients of DBA/2 spleen cells mount vigorous Mls-1 responses in vivo but their T cells retain the ability to respond to a subsequent Mls-1 challenge in vitro. We tested the possibility that the inability of DBA/2 spleen cells to inactivate Mls-1-reactive BALB/c T cells was the result of excessive costimulatory activity provided by Mls-1+ DBA/2 B cells. Costimulatory accessory cell activity has been reported to be destroyed by UV light. We exposed superantigen-presenting cells to UV radiation and found that they had lost the ability to stimulate an Mls-1 response without, however, gaining the capacity to render Mls-1-specific T cells anergic. Despite their inability to noticeably stimulate Mls-1-reactive T cells, UV-treated Mls-1+ lymphocytes induced an absolute unresponsiveness in Mls-1- recipients to a second challenge with the superantigen. Our data are in agreement with previous evidence, confirmed here, that BALB/c mice establish immunity against Mls-1+ cells, which causes the accelerated rejection of superantigen-bearing lymphocytes. Thus, our data imply that, whereas it takes stimulatory superantigenic Mtv-7 gene products to induce the activation of superantigen-reactive T cells, nonsuperantigenic Mtv-7 gene products may induce an immune response leading to the elimination of Mtv-7+ lymphoid cells.

Animals↗

PubMed1992

In vivo presentation of Mls-1 antigen by T and B lymphocytes.

Previous studies of minor lymphocyte stimulatory (Mls) presenting lymphoid cells had shown that B cells rather than T cells present stimulatory Mls-1 antigen in vitro whereas B as well as T cells present Mls-1 antigen in vivo. Deletion of Mls-1 reactive T cells in the thymus of newborn mice is induced by T cells rather than by B cells. Applying a recently developed method for measuring the Mls-1 response in Mls-1- mice we assessed the Mls-1 stimulatory activity of T and B cells quantitatively. B cells are significantly more effective than T cells in this process. Both Mls-1+ T and B cells are also capable of inducing Mls-1 anergy in Mls-1- mice. Remarkably few lymphoid cells from Mls-1+ animals are needed for this effect: a few thousand B cells or 10(4) to 10(5) T cells per mouse induce substantial Mls-1 anergy in Mls-1- mice. These low cellular requirements for Mls-1 anergy production correspond well to the low T cell requirements described for the induction of Mls-1 tolerance in newborn mice. However, the high efficacy of B cells in inducing peripheral Mls-1 anergy contrasts with their failure to induce neonatal tolerance in newborn animals. We attribute this discrepancy to the previous notion that stimulatory Mls-1 antigen is not delivered to the thymus and that B cells and T cells present qualitatively different Mls-1 related signals to Mls-1 reactive T cells.

Animals↗

PubMed1992

Regulation of T cell function by Mtv-7 gene products.

Mls-1, a superantigen encoded by the endogenous mouse mammary tumor virus Mtv-7 induces immunological tolerance through deletion of antigen-reactive T cells. A remarkable difference between this self-antigen and self-MHC antigens is that while the mouse establishes tolerance against self MHC antigens by the time of birth it does not begin to delete T cells specific for the self-superantigen until they had mounted an immuneresponse against it. An immune response occurs normally several days after birth and may be delayed experimentally for weeks before the deletion process ensues. However, for effective deletion of Mls-1 reactive T cells the mouse must be exposed to Mtv-7 positive lymphoid cells within hours after birth. In reviewing here data obtained in this and other laboratories regarding experimental induction of Mls-1 tolerance in neonatal mice we are trying to make a case for the involvement of Mtv-7 encoded antigens distinct from the superantigen. We propose that T cells reactive with non superantigenic Mtv-7 determinants pose a threat to the establishment of chimaerism between Mls-1- neonates and Mls-1+ inocula, as they may cause the rejection of Mls-1 superantigen bearing lymphocytes. Chimaerism is essential for the establishment of lasting Mls-1 tolerance.

Animals↗

PubMed1991

Induction of neonatal tolerance to the Mls-1a self-super-antigen. Time kinetics and MHC restriction.

We examined the accessibility of the thymus to a self-super-Ag encoded by the Mls-1a region of chromosome 1 and the process by which this Ag establishes immunologic tolerance. Intravenously administered Mls-1a Ag accumulates quickly in peripheral organs of adult or newborn Mls-1a- recipients, where it mounts an immune response. The Ag does not enter the thymus in detectable amounts and does not induce an immune response of Mls-1a-responsive T cells present in this organ. Instead, the thymus of newborn Mls-1a- recipients of Mls-1a+ lymphoid cells continues for several days to export Mls-1a-reactive T cells, which respond to Mls-1a Ag when they encounter it in peripheral organs. This response peaks around day 3 or day 4 and declines very rapidly thereafter. The deletion of intrathymic Mls-1a-reactive T cells ensues simultaneously with this decline. It has previously been shown that Mls-1a Ag causes deletion or anergy of Mls-1a-reactive peripheral T cells, subsequent to their activation. We see the same time kinetics in producing deletion or anergy of Mls-1a-reactive T cells in the thymus of newborn animals, with the exception that the activation phase that precedes the deletion of Mls-1a-reactive T cells occurs in the periphery and not in the thymus. This observation indicates that thymic Mls-1a-specific T cells are not deleted through activation. Whether their deletion depends on a feed-back from the peripheral activation of Mls-1a-reactive cells, as the time relationship could suggest, is not clear. The finding establishes, however, that the deletion of functionally mature Mls-1a-reactive T cells and the activation of such cells are not necessarily related events, which may or may not utilize a common trigger mechanism, such as the engagement of the TCR. Concerning the trigger mechanism, we report that Mls-1a-specific deletion of T cells is an MHC-restricted process, whereas Mls-1a-specific activation of T cells is not MHC restricted.

Animals↗

PubMed1991

A characteristic Mls-1a response precedes Mls-1a anergy in vivo.

T cells expressing V beta 6 variable gene segments of the T cell receptor undergo blast formation and divide in mice after injection of lymphoid cells bearing minor lymphocyte-stimulating (Mls)-1a gene products. This in vivo Mls-1a response resembles in vitro Mls-1a stimulation; it is dose dependent, not MHC-class II haplotype restricted, but requires expression of functional IE gene products. The in vivo Mls-1a response is followed by a complete and specific in vivo Mls-1a anergy and a partial in vitro Mls-1a anergy. The measurement of a Mls-1a response in vivo and of the establishment of in vivo anergy to it provides a convenient method to assay Mls-1a reactivity of T cells in vivo on a cell-by-cell basis in terms of cell surface phenotype, size, and mitotic activity.

Animals↗

PubMed1991

B cells control the aggregability of CD4 on T cells through continuous physical interactions.

It has previously been demonstrated that a gene on chromosome 1 in or near Mls-1 controls, on the surface of B cells, the mobility and aggregability of major histocompatibility complex (MHC) class II molecules but not the mobility or aggregability of other B-cell molecules, such as immunoglobulin (Ig) and class I antigens. We report here that this gene may also influence the aggregability of two class II antigen-reactive molecules on the surface of T cells, the T-cell receptor complex and CD4. The aggregability of the two membrane components is markedly higher on Mls-1+ T cells than on Mls-1- T cells. The properties of this phenomenon were examined in vitro as well as in vivo with particular emphasis on CD4 aggregability. It was found that, after removal of B cells, T cells lose the ability to aggregate CD4 in our standard CD4 aggregation assay. Similarly, T cells isolated from the B-cell-deficient environment of the thymus failed to aggregate CD4. Addition of B cells to either thymic T cells or B-cell-depleted peripheral T cells established CD4 aggregability within minutes. This process can be blocked with antibody against CD4 or antibody against Ia. The Mls-1 genotype predicts within the limited tests of this study the efficacy of the B-cell ability to impose a CD4 aggregation pattern on T cells: Mls-1+ B cells are markedly more effective in this respect than Mls-1- B cells. This can be demonstrated in tissue culture as well as in the animal. Similar to the Mls-1 response, this is a one-way process: Mls-1+ B cells confer to Mls-1- mice a CD4 aggregation pattern typical of the Mls-1+ mouse while Mls-1- B cells do not impose a Mls-1b-typical CD4 aggregation pattern in Mls-1a mice. Mls-1+ B cells also influence the composition of lymphocytes in the mouse. Mls-1+ mice or Mls-1- mice treated with Mls-1+ B cells have fewer T cells and more B cells in their spleen than Mls-1- animals. The gene that encodes stimulatory Mls-1 cell-surface structures has recently been identified as an endogenous mammary tumour virus (Mtv-7). We expect that the analysis of the virus genome will produce information whether the effects described here can be attributed to the virus or not.

Animals↗

PubMed1990

Immunogenic Ia-binding peptides immobilize the Ia molecule and facilitate its aggregation on the B cell membrane. Control by the M1s-1 gene.

Aggregation (e.g., through cross-linkage) of cell surface molecules is in various biologic systems a necessary event in cellular activation. Examining the Ia molecule on B cells we found that aggregation is a function of the surface Ag mobility; the higher the fraction of immobile molecules on the plane of the membrane, the better Ia forms aggregates and patches. We identify two factors that control Ia mobility and aggregability. One factor is the M1s-1a gene product; the other factor is an Ia-reactive immunogenic peptide. Both factors increase Ia aggregability and reduce the MHC Ag mobility.

Animals↗

PubMed1990

Immunogenic peptides require an undisturbed phospholipid cell membrane environment and must be amphipathic to immobilize Ia on B cells.

Ia-reactive immunogenic peptides have been shown to immobilize Ia molecules on the B cell surface and to facilitate their aggregation with specific alloantibody. We show that to immobilize Ia the peptide must be amphipathic. Polar peptides appear to bind to Ia molecules as judged by competitive inhibition, but do not immobilize the MHC molecule. This suggests the possibility that peptides establish the immobilizing membrane contact via a lipophilic group. Examining the B cell membrane lipid environment, we found that treatment of B cells with phospholipase C prevents peptide-mediated immobilization of Ia. The requirement of a lipophilic peptide portion as well as of phospholipase-sensitive membrane components for effective peptide-mediated Ia aggregation on B cell membranes suggests a role for membrane phospholipids in this process. We advance the speculation that immunodominant amphipathic peptides immobilize Ia molecules by attaching them to cell surface phospholipids which we tentatively refer to as immobilizing phospholipids.

Animals↗

PubMed1989

Synergism between HIV gp120 and gp120-specific antibody in blocking human T cell activation.

The human immunodeficiency virus (HIV) binds to CD4-positive cells through interaction of its envelope glycoprotein (gp120) with the CD4 molecule. CD4 is a prominent immunoregulatory molecule, and chronic exposure to antibody against CD4 (anti-CD4) has been shown to cause immunodeficiency in mice. T cell-dependent in vitro immune responses can also be inhibited by anti-CD4. Experimental findings reported here indicate that CD4-bound gp120 attracts gp120-specific antibodies derived from the blood of HIV-seropositive individuals to form a trimolecular complex with itself and CD4. Thus targeted to CD4, the gp120-specific antibody functions as an antibody to CD4; it cross-links and modulates the CD4 molecules and suppresses the activation of T cells as measured by mobilization of intracellular calcium (Ca2i+). The synergism between gp120 and anti-gp120 in blocking T cell activation occurs at low concentrations of both components. Neither gp120 nor anti-gp120 inhibits T cell activation by itself in the concentrations tested.

Acquired Immunodeficiency Syndrome↗

PubMed1989

Production of interleukin-1 but not tumor necrosis factor by human monocytes stimulated with pneumococcal cell surface components.

While there is considerable evidence that both interleukin-1 (IL-1) and tumor necrosis factor (TNF) are central mediators of inflammation caused by gram-negative bacteria and endotoxin, the roles of these two mediators in gram-positive infection are unknown. Pneumococcal infections are characterized by an intense inflammatory reaction in infected tissues. Current evidence suggests that the component of the pneumococcus which causes this inflammation in many body sites is the cell wall. We determined the ability of native pneumococcal cell wall, lipoteichoic acid, and cell wall subcomponents to stimulate secretion of IL-1 and TNF from human monocytes. Each pneumococcal cell surface component was found to have a different specific activity for induction of IL-1. Teichoication was an important determinant of this activity: teichoicated species were at least 10,000-fold more potent than endotoxin and 100-fold more potent than teichoic acid-free peptidoglycan. IL-1-inducing activity was greatly reduced by chemical alteration of the teichoic acid. In contrast to endotoxin, cell wall did not induce production of TNF. This dissociation of the production of IL-1 and TNF during the response of the human monocyte to pneumococcal surface components suggests that, in at least some circumstances, the mechanisms for generation of an inflammatory response to infection may be fundamentally different between gram-positive and gram-negative disease.

Cell Wall↗