Immunosuppressive Properties of α1-Microglobulin

α₁-Microglobulin (α₁m), a serum glycoprotein (26,000 d). was found to impede the proliferative response of human lymphocytes to purified protein derivative (PPD) and tetanus toxoid. The data suggest that, α₁m operates through an unstable suppressor mechanism, which no longer can function after 24 h of preculturing. This effect of α₁m on antigen stimulation did not seem to be due to binding of α₁m to PPD or cells, to altered kinetics of the PPD response, or to non-specific cytotoxicity. In contrast, PPD-induced leucocyte migration inhibition was not reversed by α₁m. α₁m did not cause significant inhibition in experiments in which lymphocytes were stimulated by the mitogens phytohaemagglutinin or concanavalin A. Finally, α₁m had its own leucocyte migration inhibitory effect.     

Isolation and Partial Characterization of a Murine Cell Surface Glycoprotein with Affinity for Exogenously Added β2-Microglobulin

Exogenously added β₂microglobulin (β₂m) binds to a variety or murine cell types. The 'receptor' for β₂m has been isolated. The purified 'receptor' comprised a 48,000-dalton chain and occasionally a 25,000-dalton component. Direct crosslinking of β₂m to the receptor on intact cells gave rise to a single 60,000-dalton β₂m-'receptor' complex. The molecular characteristics of the 'receptor' were considerably changed on binding β₂m. The size of the β₂m-'receptor' complex was increased partly due to enhanced binding of deoxycholate. The 'receptor' was less easily degraded by proteases when β₂m was bound then when free. The solubilized 'receptor' reacted with a heteroantiserum raised against H-2K and D antigens but did not exhibit any alloantigenic determinants shared with H-2 K, D or Ia antigens.     

Distribution of 'Free' and HLA-associated Human β2-Microglobulin in Some Plasma Membranes and Biological Fluids

The distribution of free and HLA-associated human β₂-microglobulin (β₂m)in serum, urine, spinal fluid, parotid duct saliva, seminal fluid, amniotic fluid and whey and in membranes from thrombocytes, lymphocytes, neutrophils and fat globules from milk was studied by crossed radioimmunoelectrophoresis (CRIE). The hydrophobic domain of HLA was demonstrable in 'charge-shift CRIE' and by binding to phenyl-Sepharose in 'hydrophobic-interaction CRIE'. In 'lectin-affinity CRIE' with concanavalin A and Lens culinaris lectin Sepharose the carbohydrate moiety present in HLA exhibited heterogeneity as judged by the appearance of two partly separated protein peaks. Except for isolated fat globule membranes, HLA-associated β₂m was present on all cells investigated. 'Free'β₂m did not contain a hydrophobic domain as assessed by charge-shirt and hydrophobic-interaction CRIE. All body fluids contained β₂m in its 'free' form only. In serum, besides the free β₂m, 2% was present is HLA-associated β₂m, which, however, did not contain a hydrophobic domain. A degradation product of 'free'β₂m, with α-mobility, was observed in sera from patients with malignant disorders, rheumatoid arthritis or systemic lupus erythematosus.     

The Interaction between Beta 2-Microglobulin (ßm) and Purified Class-I Major Histocompatibility (MHC) Antigen

The function of MHC class-I molecules is to sample peptides from the intracellular environment and present them to CD8⁺ cytotoxic T lymphocytes. To understand the molecular details of the assembly (and disassembly) of peptide-ß₂m-class-I complexes a biochemical peptidc-class-I binding assay has been generated recently and this paper reports on a similar assay for the interaction between ß₂m and class I. As a model system human ß₂m binding to mouse class I was used. The assay is strictly biochemical using purified reagents which interact in solution and complex formation is determined by size separation. It is specific and highly sensitive. The observed affinity of the interaction, K_D, is close to 0.4 nw. The rate of association at 37 C is very fasi (the k_a is around 5 × 10⁴/M/s) whereas the dissociation is slow (the k_d is around 8 × 10⁻⁶/s); the ratio of dissociation to association yields a calculated K_D close to the observed value. At 37° C almost all of the purified class I participates in binding of the exogenously offered ß₂m showing that a considerable exchange of the endogenous ß₂m occurs. Finally, it was demonstrated that exogenous ß₂m enhances binding to MHC class-I of short perfectly-matching peplides as well as longer peptides.     

Inhibition by Anti-β2-Microglobulin Antisera of Responder Cells and Not of Stimulator Cells in the Mixed Lymphocyte Reaction

Specific antisera directed against beta₂-microglobulin (β₂m) have been shown to inhibit completely the mixed lymphocyte reaction (MLR). However, the mechanism of inhibition has been unclear. In the present study, further experiments were performed to determine the effect of anti-β₂m on both the stimulator and responder cells in an MLR. The experimental design used was that of a xenogeneic MLR, using mouse and human lymphocytes. The effect of anti-human fern was studied in this system. Anti-human β₂m inhibited the xenogeneic MLR only when human lymphocytes were used as responder cells and did not inhibit the MLR when they were used as stimulator cells. These results suggest that surface β₂m is not a requirement for stimulation in an MLR; however, β₂m may be involved in the recognition of the stimulator cell by the responder cell. Although other interpretations could be invoked to explain the inhibition by anti-β₂m of the responder cell population, the one we favor is that β₂m is a part of the antigen recognition site on the responder cells.     

Mapping of the monoclonal antibody W6/32: sensitivity to the amino terminus of β2-microglobulin

Abstract: The monoclonal antibody W6/32 is one of the most commonly used pan-HLA-ABC antibodies in studying human MHC I structure and function. We have discovered that the reactivity of W6/32 is absolutely sensitive to the amino terminus of human β₂-microglobulin (hβ₂m). Bac-terially expressed recombinant forms of hβ₂m that have been extensively used in structural and biochemical studies of MHC I molecules often have an additional methionine at their amino terminus. Cell surface MHC I molecules reconstituted with allele-specific peptides and recombinant hβ₂m are reactive with various HLA-specific mAbs, but not W6/32. In contrast, cell surface HLA molecules reconstituted with peptide and native hβ₂m, which has no amino terminal methionine, are recognized by W6/32 as well as other HLA-specific mAbs. Thus, the specificity of W6/32 includes the amino terminus of hβ₂m.     

Activation of Human T and B Cells by Rabbit Anti-Human β2-Microglobulin

Rabbit anti-human β₂-microglobulin (anti-β₂m) increased the highest DNA synthesis in un-separated lymphocytes or artificially composed mixtures enriched in T and B cells. In enriched T and B cells no or low stimulation was seen. The maximal response by IgG anti-β₂m was seen in proportions of enriched T/B cells, being 3:1 for blood lymphocytes and 1:1 for spleen cells, which are the same as the physiological proportions of T and B cells in these lymphoid organs. Whereas unseparated lymphocytes gave a peat response on day 3, enriched B cells had a peak response on day 6. Fab anti-β₂m did not activate enriched T cells but increased DNA synthesis in enriched B cells to about the same extent as unseparated lymphocytes and mixtures of enriched T and B cells. The proportion of sheep erythrocyte rosette-forming cells (E-RFC) decreased after stimulation by anti-β₂m and increased after stimulation by phytohaemagglutinin. However, as revealed by autoradiography, a proportion of lymphocytes activated by anti-β₂m were E-RFC and this proportion increased with increasing stimulation by anti-β₂m. DNA synthesis induced by anti-β₂m was unchanged for spleen cells and slightly decreased for blood lymphocytes when phagocytic cells were removed by iron treatment. Supernatants from lymphocytes activated by anti-β₂m only induced low DNA synthesis in enriched T or B cells. Experiments with mitomycin treated cells indicate that cooperation and close contact between T and B cells are needed for activation by IgG anti-β₂m. T cells are needed for B cell activation by anti-β₂m and B cells are required for T cell activation to occur.     

Oligoclonality of TCRint Cells with a Low Diversity of TCR Complementarity-Determining Region 3 in Mice with Graft- Versus-Host Disease

Conventional T cells (i.e. TCR^high) are generated by the main stream of T-cell differentiation in the thymus. However, primordial T cells (i.e. TCR^int) are generated by extrathymic pathways and an alternative intrathymic pathway. Since TCR^int cells contain self-reactive clones, the diversity of the T-cell antigen receptor (TCR) complementarity-determining region (CDR) 3 was examined. The predominant Vβ8.2⁺ clones among TCR^int cells were selected for DNA sequencing. Thymectomized, irradiated mice subjected to bone-marrow transplantation (BMT) were used; graft-versus-host disease (GVHD), B6→(B6 × C3H/He) F ₁ and syngeneic BMT, B6→B6. In these combinations, only TCR^int cells were generated. Vβ8.2⁺ cells with a low diversity of CDR3 of V-gene expanded in GVHD mice. Vβ8.2⁺ cells of TCR^int and TCR^high cells in normal mice were polyclonal, showing that the former has a lower diversity of CDR3 than the latter. The clonality of activated TCR^high cells was examined, in which CD3^high cells (bm12 mice) were injected into 1 Gy-irradiated B6 nude mice. Some Vβ8.2⁺ clones among TCR^high cells were expanding but the diversity of CDR3 was greater than that of CD3^int cells, despite the fact that the recognition site of the H-2 difference was smaller. Taken together with invariant usage of Vα14, these results suggest that TCR^int cells have a low diversity of CDR3 of Vβ genes.     

Roles of Cav channels and AHNAK1 in T cells: the beauty and the beast

Summary:  T lymphocytes require Ca²⁺ entry though the plasma membrane for their activation and function. Recently, several routes for Ca²⁺ entry through the T-cell plasma membrane after activation have been described. These include calcium release-activated channels (CRAC), transient receptor potential (TRP) channels, and inositol-1,4,5-trisphosphate receptors (IP₃Rs). Herein we review the emergence of a fourth new route for Ca²⁺ entry, composed of Ca_v channels (also known as L-type voltage-gated calcium channels) and the scaffold protein AHNAK1 (AHNAK/desmoyokin). Both helper (CD4⁺) and killer (CD8⁺) T cells express high levels of Ca_v1 α1 subunits (α1S, α1C, α1D, and α1F) and AHNAK1 after their differentiation and require these molecules for Ca²⁺ entry during an immune response. In this article, we describe the observations and open questions that ultimately suggest the involvement of multiple consecutive routes for Ca²⁺ entry into lymphocytes, one of which may be mediated by Ca_v channels and AHNAK1.     

Thymic differentiation of TCRαβ+ CD8αα+ IELs

Summary:  Intraepithelial lymphocytes (IELs) contain several subsets, but the origin of the T-cell receptor (TCR)αβ⁺ CD8αα⁺ IELs has been particularly controversial. Here we provide a synthesis, based on recent work, that attempts to unify the divergent views. The intestine has a primordial function in lymphopoiesis, and precursors with the potential to differentiate into T cells are found both in the epithelium and underlying lamina propria. Moreover, the thymus has been reported to export cells to the intestine that are not fully differentiated. TCRαβ⁺ CD8αα⁺ IELs can differentiate in the intestine from each of these sources, but in normal euthymic mice, the thymus appears to be the major source for TCRαβ⁺ CD8αα⁺ IELs. This unique IEL subset is a self-reactive population that requires exposure to self-agonists for selection in the thymus, similar to other regulatory T-cell populations. IELs transition through a double-positive (DP) intermediate in the thymus, but they originate from a subset of the DP cells that can be identified by its expression of CD8αα homodimers. The agonist-selected cells in the thymus are TCRβ⁺ but CD4 and CD8 double negative. The evidence suggests that reacquired expression of CD8αα and downregulation of CD5 occur after thymus export, perhaps in the intestine under the influence of interleukin-15. As a result of agonist exposure, a new gene expression program is activated. Therefore, the increased understanding of the developmental origin of TCRαβ⁺ CD8αα⁺ IELs may help us to understand how they participate in immune regulation and protection in the intestine.     

Regulatory T cells in spontaneous autoimmune encephalomyelitis

Summary: Spontaneous experimental autoimmune encephalomyelitis (EAE) develops in 100% of mice harboring a monoclonal myelin basic protein (MBP)-specific CD4⁺αβ T-cell repertoire. Monoclonality of the αβ T-cell repertoire can be achieved by crossing MBP-specific T-cell receptor (TCR) transgenic mice with either RAG^−/− mice or TCR α^−/−/TCR β^−/− double knockout mice. Spontaneous EAE can be prevented by a single administration of purified CD4⁺ splenocytes or thymocytes obtained from wild-type syngeneic mice. The regulatory T cells (T-reg) that protect from spontaneous EAE need not express the CD25 marker, as effective protection can be attained with populations depleted of CD25⁺ T cells. Although the specificity of the regulatory T cells is important for their generation or regulatory function, T cells that protect from spontaneous EAE can have a diverse TCR α and β chain composition. T-reg cells expand poorly in vivo , and appear to be long lived. Finally, precursors for T-reg are present in fetal liver as well as in the bone marrow of aging mice. We propose that protection of healthy individuals from autoimmune diseases involves several layers of regulation, which consist of CD4⁺CD25⁺ regulatory T cells, CD4⁺CD25⁻ T-reg cells, and anti-TCR T cells, with each layer potentially operating at different stages of T-helper cell-mediated immune responses.     

Expression of α5 (CD49e) and α6 (CD49f) Integrin Subunits on T Cells in the Circulation and the Lamina Propria of Normal and Inflammatory Bowel Disease Colonic Mucosa

Intestinal lamina propria T cells are believed to be derived, via the systemic circulation, from gut-associated lymphoid tissue. After migration into the lamina propria, T cells are capable of luminally directed migration following the loss of surface epithelial cells. For adhesion and migration within the extracellular matrix, T cells are likely to utilize the integrin family of adhesion molecules. The aim of this study was to quantitatively and qualitatively investigate the expression of α₅ and α₆ integrin subunits on the surface of human T cells that: (a) migrated out of the lamina propria, (b) remained resident within the matrix and (c) were present in the circulation. In both subpopulations of CD4 and CD8-positive T cells, from both normal and inflamed (inflammatory bowel disease) colonic mucosa, there were significantly fewer α₅ and α₆-positive cells than in the peripheral blood. In addition, there were significantly fewer α₆ integrin molecules on the surface of CD4 and CD8-positive lamina propria T-cell subpopulations, compared with those in the circulation. Our studies suggest that, following migration into the lamina propria, there is down-regulation of α₅ and α₆ integrin-subunit expression on the surface of T cells. Molecules other than members of very late activation antigen-5 (VLA-5) (α₅β₁) and VLA-6 (α₆β₁) families of adhesion molecules are likely to be important in interactions with extracellular components in the lamina propria of normal and inflamed human colonic mucosa.     

The Complete Amino Acid Sequence of Rat β2-Microglobulin

The primary structure of rat β₂-microglobulin (β₂m) was determined. It is a polypeptide of 99 amino acids with the following sequence: IQKTPQIQVY SRHPPENGKP NFLNCYVSQF HPPQIEIELL KNGKKIPNIE MSDLSFSKDW SFYILAHTEF TPTETDVYAC RVKHVTLKEP KTVTWDRDM. The primary structure was determined by NH₂-terminal sequence analysis together with sequence determination of one cyanogen bromide fragment and one tryptic peptide. Of other known β₂m sequences, rat β₂m is most homologous to mouse β₂m (83% identity). The rabbit, human, and guinea pig sequences are more distant, with 24,27, and 31% differences, respectively.     

Complexes in Human Plasma between α1-Antitrypsin and IgA, and α1-Antitrypsin and Fibrinogen

Crossed immunoelectrophoretic analyses revealed that plasma contains a complex between α₁-antitrypsin¹ and IgA. Normally the complex constitutes 1–2% of these proteins. The amount varies mainly with the IgA and to some extent with the α₁-at content of the plasma. The complex is sensitive to thiol reagents and is reduced in vivo by penicillamine. The size of the complex and the amount of reduction products are compatible with the assumption of 1 IgA monomer or dimer per α₁-at molecule. An α₁-at complex with fibrinogen is also a regular plasma constituent. This complex is not susceptible to thiol reagents.     

γδ T-Cell Precursor-Derived CD4− CD8−αβ T Cells Retain γδ Cell Function

We have previously shown that some of the DNαβ⁺ T cells arising in TcRα-chain transgenic mice are of γδ T cell origin, based on phenotypic data and on their status of TcR gene rearrangements. In the present report we investigated the impact of αβ TcR expression on the functional programme of the mature γδ precursor-derived DNαβ⁺ T cells. Our results demonstrate that both their proliferative capacity and their cytokine production profile are similar to that of γδ T cells. Furthermore, both transgenic DNαβ⁺ T cells and DNγδ⁺ T cells up-regulate CD8α expression after activation, but, in contrast to CD4⁺αβ T cells, are unable to induce proliferation of naive B cells. Thus, our results suggest that the effector functions of mature T cells are determined independently of the TcR isotype, probably at an early stage of differentiation, and thereby have important implications for current models of T-cell lineage commitment.     

Immunohistochemical Investigation of Vimentin, Neuron-specific Enolase, α1-antichymotrypsin and α1-antitrypsin in Adenoid Cystic Carcinoma of the Salivary Gland

Fifty-four adenoid cystic carcinomas (ACC) arising in major and minor salivary glands as well as in normal salivary glands were studied by immunohistochemistry for the presence of vimentin, neuron specific enolase (NSE), α₁-antichymotrypsin (α₁-ACT) and α₁-_- antitrypsin (α₁-_- AT). Five patterns of histological differentiation were found in ACC, and for the cellular components of each, it was possible to establish a special immunohistochemical profile. In ACC, vimentin-positive cells were observed in the outer tubular, cyst-lining and small angular cells. NSE was positive in the myoepithelial cells of normal salivary gland. Neoplastic cells of ACC showed NSE positivity mainly in the small angular cells and partly in the duct luminal cells. α₁-ACT was localized in the intercalated duct cells and serous acinar cells of normal salivary gland, and in the duct luminal cells of ACC. α₁-AT could not be detected in any of the epithelial cells of normal salivary gland. In ACC, eosinophilic hyaline material in the cribriform spaces was positive for α₁-AT, but no positivity was demonstrated in tumor cells. The present study showed that there are at least two populations of tumor cells in ACC: duct luminal cells that express α₁-ACT, thus indicating their ductal character, and small angular cells that express vimentin, characteristic of non-luminal cells. Moreover, our results indicate that α₁-AT is a useful marker of basement membrane-like material.     

CD3−4−8− Thymocyte Precursors with Interleukin-2 Receptors Differentiate Phenotypically in Coculture with Thymic Stromal Cells

CD3⁻4⁻8⁻ interleukin-2 receptor positive (IL-2R⁺) thymocyte precursors from adult mice were cocultured with thymic stromal cells from syngeneic adult mice. The IL-2R⁺CD3⁻4⁻8⁻ thymocytes were obtained by positive panning of IL-2R⁺ cells followed by either sorting or negative panning of triple negative cells, and they were cocultured with primary or secondary cultures of heterogeneous thymic stromal cells. Phenotypic maturation of these precursor cells was extremely rapid. Within 2½ days significant numbers of CD4⁺8⁺ and CD3⁺4⁺8⁻ cell populations developed, the latter expressing the αβ T-cell receptor (αβ-TCR). Thus heterogeneous stromal cell cultures support the development of IL-2R⁺ precursors and with these methods it will now be possible to isolate the particular stromal cells involved at each stromal-dependent step.     

Lack of Expression of HLA Antigens on Choriocarcinoma Cell Lines

A panel of monoclonal antibodies against HLA–A, B, C, DRw, β₂m and other determinants on human cells has been used in indirect trace binding and absorption assays to determine the distribution of these antigens on choriocarcinoma cell lines. HLA–A, B, C, DRw and β₂ m were not found on these cell lines, while other human antigens expressed on most human tissues were expressed on all the lines.     

CD8alpha+beta(low) effector T cells in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder characterized by the loss of self-tolerance to nuclear antigens. Aberrant T-cell function plays a central role in lupus pathogenesis. We and others previously demonstrated that peripheral TCRαβ⁺CD3⁺ T cells express CD8β either at a high (CD8β^high) or low density (CD8β^low), thereby defining two functionally distinct subsets. CD8β^low T cells express predominantly CD8αα and less CD8αβ as a coreceptor, display a differentiated phenotype and exert effector function. CD8β^high T cells appear to be the precursors expressing predominantly the heterodimeric efficient CD8αβ coreceptor, exhibiting a naïve phenotype and high proliferative capacity. In the present study, the distribution and functional properties of CD8β^high and CD8β^low T cells of SLE patients were compared ( n  = 20) with those of healthy subjects ( n  = 16). It was found that expansion of CD8β^low T-cell subset correlated with disease activity indicating chronic antigenic stimulation leading to a major lack of naïve CD8β^high precursor T cells in SLE. Functional characteristics of CD8β^low T cells including production of cytokines and cytotoxic granules were not significantly different between patients with SLE and healthy individuals. We speculate that unbalanced CD8β^high/CD8β^low T-cell relation reflects a skewed homeostasis within the CD8⁺ T-cell compartment towards fully differentiated effector T cells possibly due to persistent antigen stimulation in SLE.