Transection of major histocompatibility complex class I-induced neurites by cytotoxic T lymphocytes.

Damage to neurites with transection of axons and spheroid formation is commonly noted in the central nervous system during viral and autoimmune diseases such as multiple sclerosis, but it remains open whether such changes are caused primarily by immune mechanisms or whether they are secondary to inflammation. The present experiments explored whether neurites can be directly attacked by cytotoxic T lymphocytes (CTLs). Cultured murine neurons induced by interferon-gamma and tetrodotoxin to express major histocompatibility complex class I were pulsed with a dominant peptide of the lymphochoriomeningitis virus envelope glycoprotein (GP33) and then confronted with GP33-specific CD8(+) CTLs. Within 3 hours the neurites developed cytoskeleton breaks with adjacent solitary neuritic spheroids, as documented by confocal examination of the cytoskeletal marker beta-tubulin III. At the same time cytoskeleton staining of the neuronal somata showed no damage. The CTLs selectively attacked neurites and induced segmental membrane disruption 5 to 30 minutes after the establishment of peptide-specific CTL-neurite contact, as directly visualized by live confocal imaging. Thus, major histocompatibility complex class I/peptide-restricted CD8(+) T lymphocytes can induce lesions to neurites, which might be responsible for axonal damage during neuroinflammatory diseases.     

The alpha 3 domain of major histocompatibility complex class I molecules plays a critical role in cytotoxic T lymphocyte stimulation

Allogeneic major histocompatibility complex class I molecules induce strong cytotoxic T lymphocyte (CTL) responses whereas xenogeneic molecules do not. We have tested a series of mouse/human hybrid molecules for their ability to stimulate mouse CTL. The molecules with murine alpha 3 domains consistently stimulated stronger CTL responses than those with human alpha 3 domains, independent of the species origin of the N-terminal alpha 1 or alpha 2 domains. We have found that the ability of class I molecules to induce strong cytotoxic responses correlates positively with their ability to stimulate expansion of the CD8+CD4-T cell subset. The results indicate that mouse T cells can recognize class I molecules with human alpha 1 and/or alpha 2 domains, but for efficient stimulation of these T cells it is important that the immunizing molecule contains a murine alpha 3 domain. We suggest that T cell priming requires an efficient interaction of CD8 with the class I alpha 3 domain, and this shows some species restriction.     

Resting porcine T lymphocytes expressing class II major histocompatibility antigen.

The immune system of swine is unique in that the expression of CD4 and CD8 antigens defines four subpopulations of resting, extrathymic (CD1-) T lymphocytes in the circulation as well as in lymphoid tissue. Here it is documented that the specialty of the porcine T lymphocyte compartment extends to the expression of class II MHC (SLA) antigens. While the TCR gamma/delta CD4-CD8- as well as the TCR alpha/beta CD4+CD8- subpopulation both lack MHC II, the TCR alpha/beta CD4-CD8+ and the CD4+CD8+ subpopulation, the latter of which is private to swine, both do express MHC II. As opposed to human T lymphocytes, expression of porcine MHC II is not transient and restricted to lymphoblasts but is imminent in small, resting T lymphocytes of the two CD8-expressing subsets, even though also in swine activation can induce MHC II. Activation-induced extrathymic acquisition of MHC II without reversal can be discussed as one possible way of how MHC II+ T lymphocytes are generated. Alternatively, MHC II antigens should already be expressed by thymic progenitors. Remarkably, all CD1+CD4-CD8+ and most CD1+CD4+CD8+ thymocytes lack MHC II, yet, a minor subset with the phenotype CD4hiCD8hi expresses MHC II. One may speculate that these cells do not undergo thymic selection and represent the progenitors of the unusual, swine-typic MHC II+CD4+CD8+ extrathymic T lymphocytes.     

Complexity in the major histocompatibility complex.

The human major histocompatibility complex (MHC) is one of the most intensively studied regions of the human genome, containing over 70 known genes and spanning about 4 million base pairs (4 Mbp) of DNA on chromosome 6p21.3 (Klein, 1986). It can be divided up into three regions: the class I region (telomeric), the class II region (centromeric), and the class III region (between class I and II), which includes the complement component genes C2, C4, and Bf (Trowsdale & Campbell, 1988). The MHC has been mapped in detail using pulse field gel electrophoresis (PFGE) and by cloning in yeast artificial chromosome (YAC) and cosmid vectors, revealing long stretches of DNA between the regions as well as between individual class I and class II genes. Novel genes, that have no sequence relationships with class I, class II or complement components, have recently been found in these areas, and we will present an update on these after reviewing the more established loci.     

Phenotypical and functional characterization of Herpesvirus saimiri-immortalized human major histocompatibility complex class ll-deficient T lymphocytes

Abstract: CD8⁺ T lymphocytes from two unrelated cases of MHC class II deficiency were immortalized in vitro using Herpesvirus saimiri. In both cases, a lack of expression of surface MHC class II molecules was ascertained, whereas variable defects were shown for MHC class I, CD74 (invariant chain) and LAG-3 (an MHC class II ligand). The functional analysis of both H. saimiri -immortalized T-cell lines revealed the existence of a proliferation impairment in response to anti-CD3 but not to other surface or transmem-brane stimuli. Further characterization of this functional defect indicated that it was not associated with impaired early activation events (like calcium flux) but, rather, with certain late events, like the induction of IL-2. H. saimiri '-immortalized T cells may be valuable in studying the biological role of MHC class II molecules in activated human T cells.     

T cell development in a major histocompatibility complex class II-deficient patient

In this report we show that the major histocompatibility complex (MHC) class II-negative thymus of a bare lymphocyte syndrome (BLS) patient contains a reduced CD4⁺ CD8^? T cell population when compared to thymocytes derived from a MHC class II-expressing thymus. Of these CD4⁺ CD8^? BLS thymocytes, approximately only one third co-expressed the CD3 antigen, moreover at a lower expression level when compared to control thymocytes. This suggests a partial maturation of the CD4⁺ CD8^? T cells in the absence of MHC class II expression. Among the BLS thymocytes, CD4⁺ CD8⁺ thymocytes could easily be detected. Noteworthy, the number of CD4^? CD8⁺ thymocytes was significantly increased. CD4⁺ CD8^? T cells could also be found among the BLS peripheral blood mononuclear cells, albeit at reduced numbers. Despite the absence of peripheral MHC class II expression, the majority of these CD4⁺ CD8^? T cells co-expressed the CD45RO marker. In the BLS patient, thymocytes as well as peripheral CD4⁺ CD8^? T cells were not restricted in the use of the available T cell receptor (TcR) V gene family pool. However, the lack of detectable levels of thymic and peripheral MHC class II antigen expression in the BLS patient had altered the CD4^?skewing patterns of TcR V gene families which were present in normal individuals. In conclusion, the lack of MHC class II expression in the BLS patient does not completely inhibit the CD4+ CD8^? T cell development.     

A role for the Hsp90 molecular chaperone family in antigen presentation to T lymphocytes via major histocompatibility complex class II molecules

The heat shock protein (HSP) Hsp90 is known to chaperone cytosolic peptides for MHC class I (MHCI)-restricted antigen presentation to T lymphocytes. We now demonstrate a role for Hsp90 activity in presentation of antigens on MHCII. Treatment of mouse antigen-presenting cells (APC) with the pharmacological Hsp90 inhibitor, geldanamycin, inhibited MHCII-mediated presentation of endocytosed and cytosolic proteins as well as synthetic peptides to specific T cells. Ectopic expression of human Hsp90 in APC enhanced MHCII-mediated antigen presentation. Further, pharmacological Hsp90 inhibition reduced, while retroviral Hsp90 overexpression enhanced, the levels of stable compact MHCII heterodimers correlating with the antigen presentation phenotype. Pharmacological inhibition of Hsp90 activity in IFN-gamma-treated APC resulted in severe abrogation of MHCII-restricted presentation of cytosolic antigen, but only partially inhibited exogenous antigen presentation. Our data suggest a major role for Hsp90 activity in MHCII-mediated antigen presentation pathways, and implicate IFN-gamma-inducible Hsp90-independent mechanisms.     

Rabbit major histocompatibility complex. IV. Expression of major histocompatibility complex class II genes

The rabbit MHC class II DP, DQ, and DR alpha and beta chain genes were transfected into murine B lymphoma cells. The transfected cells expressed R-DQ and R-DR molecules on the cell surface but they did not express the R-DP genes either on the cell surface or at the level of mRNA. Northern blot analyses showed that the R-DP genes were expressed, albeit at low levels, in rabbit spleen. Similar analyses showed that the R-DQ and R-DR genes were expressed at high levels in rabbit spleen. A new monoclonal anti-rabbit class II antibody, RDR34, has been developed and shown to react with the R-DR transfected cells and not with the R-DQ transfected cells. The previously described monoclonal anti-rabbit class II antibody, 2C4, reacted with the R-DQ transfected cells and not with the R-DR transfected cells. Thus, 2C4 and RDR34 MAb's are specific for the R-DQ and R-DR molecules, respectively. Each of the antibodies reacted with approximately 50% of rabbit spleen cells as shown by immunofluorescent antibody studies.     

Diseases caused by reactions of T lymphocytes to in compatible structures of the major histocompatibility complex. I. Autoimmune hemolytic anemia

The capacities of various lymphoid cells from C57BL/10 donors to induce antibodies against red blood cells (RBC) in (C57BL/10 × DBA/2)F₁ recipients were compared: cortisone-resistant thymocytes were more potent inducers than spleen cells, and bone marrow cells were ineffective. This established a need for parental T lymphocytes in the induction of Coombs-positive hemolytic anemia by the graft-versus-host reaction (GVHR). Since some of the anti-RBC antibodies carried the Ig^c allotype specific for the F₁ host, they were autoantibodies. When antibodies were eluted from the erythrocytes of F₁ mice undergoing the GVHR (GVH F₁ mice) and subsequently tested against normal RBC in the indirect Coombs' test, the Ig^c allotype was demonstrable even on those antibodies found to react with RBC of the donor strain (C57BL/10). In addition, reactions with normal intact RBC of other strains and species were noted. Anti-RBC antibodies belonged to all Ig classes and subclasses that were tested (IgG₁, IgG_2a, IgG_2b, IgA, and IgM). By means of histocompatibility typing it was shown that the overwhelming majority of lymphoid cells from GVH animals were host cells; most of these host cells were Thy-1.2-negative. In several GVH F₁ mice Coombs-positive erythrocytes were demonstrated for periods of more than 5 months; Ig^c-positive anti-RBC antibodies were detected for periods up to 3 months. When an additional injection of parental T cells was administered to GVH F₁ mice, which had become Coombs-negative in the course of the GVHR, new anti-RBC antibodies appeared. In contrast to F₁ B cells, T cells of the F₁ host were not needed for autoimmunization as shown by the induction of anti-RBC auto-antibodies in F₁ recipients that were depleted of autologous T cells prior to the administration of parental T cells. When (C57BL/10 × DBA/2)F₁ mice were back-crossed into strain C57BL/10 and the offsprings injected with C57BL/10 (H-2^bb) lymphoid cells, most of the H-2 heterozygous (H-2^bd) back-crosses developed Coombs'-positive hemolytic anemia, whereas none of the H-2 homozygous (H-2^bb) ones did. The most likely explanation of these results is that anti-RBC autoantibodies were induced by a persistent reaction of parental T helper cells to incompatible H-2 structures on normally present autoreactive F₁ B cells. The hypothesis is proposed that reactions of T lymphocytes against virally or chemically altered structures of the major histocompatibility complex may lead to autoimmunization also in nonchimeric individuals.     

Thymic nurse cell lymphocytes react against self major histocompatibility complex

It has been postulated that thymic nurse cells (TNC), lymphoid-epithelial complexes composed of thymocytes enclosed within major histocompatibility complex (MHC) class I⁺ and class II⁺ cortical epithelial cells, may provide an optimal microenvironment for the process of T cell selection. By transplanting single TNC in the avian chorionallantoic membrane assay we demonstrate that a significant portion of intra-TNC lymphocytes (TNC-L) possess reactivity against self-MHC molecules. The frequency of these autoreactive cells among TNC-L exceeds by far that of thymocytes or peripheral blood lymphocytes of the same donor. These results indicate that TNC-L constitute a T cell population enriched for self-MHC reactivity, i.e. cells that have undergone positive selection, but not yet deletion and/or deactivation.     

Diseases caused by reactions of T lymphocytes to incompatible structures of the major histocompatibility complex. IV. Autoantibodies to nuclear antigens.

We studied the requirements for induction of ANA formation in non-irradiated F1 hybrid mice undergoing a chronic graft-versus-host reaction (GVHR) after the injection of parental-strain lymphocytes. T lymphocytes in the donor cell inoculum were both needed and sufficient for the induction of ANA formation. For optimal ANA formation, the F1 recipient mice had to differ at H-2 from the parental donor strain. ANA belonged to the IgG1, IgG2, IgM and IgA (sub)classes of immunoglobulin. IgG ANA occurred in maximal serum titres of 1 in 5,120. ANA were not donor anti-host alloantibodies. At least some ANA were true autoantibodies, i.e. of F1 origin, because they carried the Ig allotypic markers characteristic of the F1 hybrid recipients. These findings are consistent with the concept that the pathogenic mechanism underlying autoantibody formation during the GVHR is an abnormal T-B-cell co-operation. In this process, donor T cells react against foreign histocompatibility antigens of the F1 recipient and generate non-specific help for B cells, including the autoreactive B cells.     

Autoimmunity in non-human primates: the role of major histocompatibility complex and T cells, and implications for therapy.

Two autoimmune disease models were studied in rhesus monkeys: type II collagen-induced arthritis (CIA) and experimental allergic encephalomyelitis (EAE). Unrelated outbred animals were used in these studies. In both models disease resistant and susceptible individuals could be identified. Susceptibility correlated with in vitro cellular responsiveness to antigen in the CIA model. In both models resistant as well as susceptible individuals developed a humoral response to the inducing antigen. However, there is an indication that IgM antibodies play a crucial role in the induction of CIA. No clear association between major histocompatibility complex (MHC) type and disease incidence was found although a higher frequency of a certain DR type was observed in EAE susceptible monkeys. It is likely that both the antigen binding capacity of the MHC class II molecules and the T-cell repertoire play an important role in determining whether disease will develop or not.     

T cell receptor specificity for major histocompatibility complex proteins

The ligands for alpha beta T cell receptors (alphabetaTCRs) are usually major histocompatibility complex (MHC) proteins bound to peptides. Although there is evidence that T cell receptor variable regions have been selected evolutionarily to bind MHC, the rules governing this interaction have not previously been apparent. However, recent solved structures of T cell receptors with related variable regions bound to MHC plus peptides suggest that some amino acids in variable region CDR1 and CDR2s almost always react in a consistent way with MHC. These amino acids may therefore have been selected evolutionarily to predispose T cell receptors toward recognition of MHC ligands.     

Structural basis for a major histocompatibility complex class Ib-restricted T cell response

In contrast to antigen-specific immunity orchestrated by major histocompatibility complex (MHC) class Ia molecules, the ancestrally related nonclassical MHC class Ib molecules generally mediate innate immune responses. Here we have demonstrated the structural basis by which the MHC class Ib molecule HLA-E mediates an adaptive MHC-restricted cytotoxic T lymphocyte response to human cytomegalovirus. Highly constrained by host genetics, the response showed notable fine specificity for position 8 of the viral peptide, which is the sole discriminator of self versus nonself. Despite the evolutionary divergence of MHC class Ia and class Ib molecules, the structure of the T cell receptor-MHC class Ib complex was very similar to that of conventional T cell receptor-MHC class Ia complexes. These results emphasize the evolutionary 'ambiguity' of HLA-E, which not only interacts with innate immune receptors but also has the functional capacity to mediate virus-specific cytotoxic T lymphocyte responses during adaptive immunity.     

Induction of cytotoxic T lymphocytes specific to the molecule of the class I major histocompatibility complex for subcutaneous immunization in pads

T lymphocytes from immune lymph nodes, specific to the molecule of the class I major histocompatibility complex, were found to contain cytotoxic T lymphocyte precursors which mature to become effector cytotoxic T lymphocytes only in the presence of helper cells and L3T4⁺, but not Lyt2⁺ T helpers. The findings indicate that a subcutaneous injection of alloantigen of the class I major histocompatibility complex for immunization in the pads leads to the creaction of the type of microenvironment of the lymph nodes which prevents activation of Lyt2⁺ T helpers or leads to the activation of their functionally negligible part. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 119, N ^o 2, pp. 190–193, February, 1995 Presented by N. N. Trapeznikov, Member of the Russian Academy of Medical Sciences     

Engagement of a T cell receptor by major histocompatibility complex irrespective of peptide

T cell receptors (TCR) identify target cells presenting a ligand consisting of a major histocompatibility complex molecule (MHC) and an antigenic peptide. A considerable amount of evidence indicates that the TCR contacts both the peptide and the MHC components of the ligand. In fully differentiated T cells the interaction between the peptide and the TCR makes the critical contribution to eliciting a cellular response. However, during the positive selection of thymocytes the contribution of peptide relative to MHC is less well established. Indeed it has been suggested that the critical interaction for positive selection is between the TCR and the MHC molecule and that peptides can be viewed as either allowing or obstructing this contact. This predicts that a given TCR is capable of engaging multiple MHC/peptide complexes. In this study a system is described which detects simply engagement of the TCR by MHC/peptide complexes rather than the functional outcome of such interactions. Using this approach the extent to which peptides can influence contacts between the TCR and the MHC molecule has been examined. The results show that the TCR does in fact engage a wide range of ligands in an MHC-restricted but largely peptide-independent manner, suggesting that only a few peptides are able to prevent the TCR from contacting the MHC molecule.