Classical Antigen Presentation Research Articles

In contrast to specific B cells, human basophils are unaffected by the toxic activity of an allergen toxin due to lack of internalization of immunoglobulin E‐bound allergen

Specific immunotherapy is the only curative therapy for type I allergies and the alarming increase in allergy prevalence emphasizes the need for additional/alternative strategies for curative treatment. Allergen toxins (AT), fusion products of an allergen with an apoptosis inducing cytotoxin, are a new kind of immunotoxin. AT should allow allergen-specific targeting and elimination of allergy-relevant cells, with B cells being the primary target. An important question is the fate of the effector cells, e.g. mast cells and basophils, which carry allergen-specific IgE: the immunotoxin might even prove to be harmful. We established a reliable in vitro B cell model (using two mouse hybridoma cell lines) for testing specificity and toxicity of P5-ETA', a fusion protein of the major timothy grass pollen allergen Phl p 5b and truncated Pseudomonas Exotoxin A. In a second step, we investigated the impact of the AT on human basophils. P5-ETA' reliably eliminated Phl p 5-specific cells in the in vitro B cell model, leaving unspecific B cells unharmed. Human basophils of grass pollen allergic donors specifically bound P5-ETA', released IL-4 and up-regulated the activation marker CD203c, but were not subject to the toxic effect because of lack of internalization of IgE-bound allergen. According to our data, basophils are pure effector cells in the context of IgE-bound allergen and not involved in classical antigen presentation.

Noncovalent interactions of drugs with immune receptors may mediate drug-induced hypersensitivity reactions

Drug-induced hypersensitivity reactions are instructive examples of immune reactions against low molecular weight compounds. Classically, such reactions have been explained by the hapten concept, according to which the small antigen covalently modifies an endogenous protein; recent studies show strong associations of several HLA molecules with hypersensitivity. In recent years, however, evidence has become stronger that not all drugs need to bind covalently to the major histocompatibility complex (MHC)-peptide complex in order to trigger an immune response. Rather, some drugs may bind reversibly to the MHC or possibly to the T-cell receptor (TCR), eliciting immune reactions akin to the pharmacological activation of other receptors. While the exact mechanism is still a matter of debate, noncovalent drug presentation clearly leads to the activation of drug-specific T cells. In some patients with hypersensitivity, such a response may occur within hours of even the first exposure to the drug. Thus, the reaction to the drug may not be the result of a classical, primary response but rather be mediated by existing, preactivated T cells that display cross-reactivity for the drug and have additional (peptide) specificity as well. In this way, certain drugs may circumvent the checkpoints for immune activation imposed by the classical antigen processing and presentation mechanisms, which may help to explain the idiosyncratic nature of many drug hypersensitivity reactions.

Regulation of CD1d expression by murine tumor cells: Escape from immunosurveillance or alternate target molecules?

alpha beta+ TCR T cells recognize peptide fragments displayed by MHC-class I or -class II molecules. Recently, additional mechanisms of antigen recognition by T cells have been identified, including CD1-mediated presentation of nonpeptide antigens. Only a limited number of CD1 antigens is retained in the mouse, i.e., the group II CD1 antigens, which are split into CD1D1 and CD1d2. Several T cell subsets have been shown to interact with murine CD1 antigens, including NK cells or "natural T cells" with the invariant V alpha 14 J alpha 281 TCR chain. Even if TAP defects may prevent classical endogenous antigen presentation in tumor cell lines, antigen presentation via CD1 is still functional. Therefore, CD1-mediated recognition of transformed cells by NK cells or "natural T cells" may represent an alternative way for immune surveillance. CD1 cell surface expression in murine tumor cell lines of different histology, including the B cell lymphoma A20, macrophage cell lines J774 and P388D1, mastocytoma P815, thymoma EL-4, melanoma B16, colon adenocarcinoma MC-38 and renal carcinoma Renca is regulated by Th1- (IFN-gamma), Th2- (IL-4, IL-10 and vIL-10) or GM-CSF (Th1/Th2) cytokines, depending on the tumor histology. In order to distinguish between CD1D1 and CD1d2 molecules, we examined differential expression of these CD1 isoforms by ratio RT-PCR: A20, EL-4, P815 and MC-38 cells exclusively express CD1D1 transcripts but not CD1D2 mRNA independent of cytokine treatment. Decreased CD1d expression leads to reduced immune recognition of CD1d+ tumor cells by freshly isolated NK1.1(+) effector cells as defined by cytolysis and IFN-gamma release. Thus, modulation of CD1 expression on tumor cells by cytokines may be advantageous to drive cellular anti-tumor antigen directed immune responses directed against TAP-independent, non-classical MHC restricting molecules.

Bacterial infections and atopic dermatitis.

Bacterial infections and atopic dermatitis.

CD91 Is a Common Receptor for Heat Shock Proteins gp96, hsp90, hsp70, and Calreticulin

Complexes of the heat shock protein gp96 and antigenic peptides are taken up by antigen-presenting cells and presented by MHC class I molecules. In order to explain the unusual efficiency of this process, the uptake of gp96 had been postulated to occur through a receptor, identified recently as CD91. We show here that complexes of peptides with heat shock proteins hsp90, calreticulin, and hsp70 are also taken up by macrophages and dendritic cells and re-presented by MHC class I molecules. All heat shock proteins utilize the CD91 receptor, even though some of the proteins have no homology with each other. Postuptake processing of gp96-chaperoned peptides requires proteasomes and the transporters associated with antigen processing, utilizing the classical endogenous antigen presentation pathway.

Epithelial cell antigen presentation

For decades intestinal epithelial cells were thought of as passive barriers to luminal contents, cells involved in nutrient absorption and electrolyte secretion. Studies during the past 10 to 15 years have changed that concept as our understanding of mucosal immunity has evolved and as we have come to understand that the regulation of this system is unique in terms of cellular interactions and factors produced. The intestinal epithelial cell has moved to the forefront of these studies where it has been shown to be an active participant in mucosal immunoregulation and inflammation. Results of the earliest studies suggested that epithelial cells might be involved in immune regulation because they expressed a series of cell surface molecules that correlate with classical antigen presentation (class I and II MHC molecules). Later on, the expression of nonclassical class I molecules was identified on these cells as well, raising the possibility of novel forms of interactions with unique cell populations. This was followed by the observation that epithelial cells secrete cytokines and chemokines, which not only regulate mucosal immune responses but also regulate inflammatory responses. By such processes, the IEC has been proposed as being a bridge between innate and adaptive immunity. The recent description of Toll-like receptors on IECs adds further support to this concept. Clearly there is growing appreciation of the multifaceted role that the IEC plays in the gut. The work on IECs in the past year has helped to refine this role.

Major histocompatibility complex class I viral antigen processing in the secretory pathway defined by the trans-Golgi network protease furin.

Classical antigen presentation by major histocompatibility complex class I molecules involves cytosolic processing of endogenously synthesized antigens by proteasomes and translocation of processed peptides into the endoplasmic reticulum (ER) by transporters associated with antigen presentation (TAP). Alternative pathways for processing of endogenous antigens, generally involving the ER, have been suggested but not fully proved. We analyzed the potential for class I presentation of proteolytic maturation of secretory antigens in the exocytic pathway. We found that hepatitis B (HB) virus secretory core protein HBe can efficiently deliver COOH-terminally located antigenic peptides for endogenous class I loading in the absence of TAP. Antigen presentation to specific cytotoxic T lymphocytes correlates with protein maturation at the COOH terminus, since modification of maturation and transport of HBe through the secretory pathway alters antigen presentation. Both maturation and a necessary processing step occur in the Golgi or post-Golgi compartment. Antigen presentation is independent of proteasome activity, but inhibitors of the trans-Golgi network resident protease furin inhibit both HBe maturation and antigen presentation. These results define a new antigen processing pathway located in the secretory route, with a central role for proteolytic maturation mediated by the subtilisin protease family member furin as an efficient source for antigen presentation.

Genetic analysis of the essential components of the immunoprotective response to infection with Eimeria vermiformis

The immune responses generated after infection with Eimeria spp. are complex, include both cellular and humoral components, and lead to protection against re-infection. To facilitate the rational development of the next generation of anticoccidial vaccines it is important that the nature of the immunoprotective response against infection with Eimeria spp. is determined. In this brief report we discuss results that were obtained using a combination of genetic and cellular approaches to dissect the essential immune effector components that operate against infection with Eimeria vermiformis. Mice rendered deficient of immune function by targeted gene disruption at a variety of immune loci represent an integral component of our studies and include those with targeted gene disruption at loci that encode the B- and T-cell receptors (BCR, TCR), antigen presentation molecules and immune-effector molecules. Our studies demonstrated that TCR αβ T cells are essential for immunoprotection during both primary and secondary infection. Moreover, during primary infection the major effector cell type is a population of major histocompatibility complex class II-restricted, interferon-g-producing TCR αβ T cell consistent with a T helper 1 phenotype. In addition, there is a supplementary role for another class of cells (presumably T cells) that are restricted to either non- classical antigen presentation molecules or classical major histocompatibility complex class I loaded via an atypical pathway. Mice with a deficiency in interleukin-6 were slightly more susceptible to primary infection than intact animals, consistent with the reported effects of interleukin-6 upon the generation of T helper 1-type responses in vivo. In terms of the host response to re-infection, TCR αβ T cells were essential for immunity, but the requirement for specific cell subsets and effector mechanisms was much less stringent. Mice deficient in gd T cells, classical major histocompatibility complex class I, non-classical antigen presentation pathways, the cytokines interferon-g, interleukin-4, interleukin-6 and the cytolytic effector molecules perforin or FasL were completely immune to secondary infection. Moreover, major histo-compatibility complex class II-deficient I-A β– \\ – mice were capable of mounting a substantial response to secondary infection, manifest by a 95% reduction in oocyst output compared with primary infection. These data have important consequences for the development of immune intervention strategies and indicate that vaccine development may be targeted toward the generation of a wider range of effector mechanisms than those that operate during primary infection.

Class II MHC expression on rat intestinal intraepithelial lymphocytes

The expression of class II major histocompatibility complex (MHC) on rat intestinal intraepithelial lymphocytes (IELs) and mesenteric lymph node cells (MLNCs) were examined by immunofluorescence and flow cytometry. As expected, MLNCs contain eight small populations of CD4 + class II MHC + T-cells in addition to classical antigen presenting cells. In contrast, rat IELs include a significant population of class II MHC + T-cells, predominantly in the CD8 +CD4 −αβTCR + subset. IEL samples with a relatively high percentage of class II MHC + cells also include some CD4 + class II MHC + cells; IEL samples with a low percentage of class II MHC + cells also include some CD4 −CD8 − class II MHC + cells. The role of lymphocyte subpopulations in the intestinal epithelium may need to be revisited in consideration of these findings.

Reiter's syndrome and reactive arthritis: A current view

This paper reviews advances in the understanding of the pathogenesis of reactive arthritis that have occurred over the last decade. Inflammatory aseptic joint disease has been linked with prior infection initiated by many different species of microorganisms. The presence of intra-articular bacterial antigens has now been firmly established with the demonstration of bacteria, bacterial fragments, DNA, RNA, and bacterial lipopolysaccharide in joints of patients with reactive arthritis. Chlamydia trachomatis, Salmonella enteritidis, and Shigella flexneri have all been detected in the joint by immunological techniques, although there is still some doubt as to the form in which they reach the joint and whether or not they persist. A number of phlogistic bacterial components could be acting as arthritogens. Negative joint culture results from patients with reactive arthritis make it unlikely that bacteria in the joint are viable, although chlamydial DNA has been shown in the joints of patients with sexually acquired reactive arthritis using the polymerase chain reaction. The use of antimicrobial therapy in the treatment of reactive arthritis is under review; data suggests that long-term antibiotic treatment warrants further study. The role of HLA-B27 in disease pathogenesis is discussed as are possible mechanisms of interplay between germ and gene. HLA-B27 might confer disease susceptibility by affecting immune mechanisms other than classical antigen presentation. The immunopathogenesis of joint inflammation in reactive arthritis is explored with reference to studies of humoral and cellular immune responses. Serological evidence to support the concept of molecular mimicry is far from conclusive; the results of relevant studies are summarized. Lymphocyte proliferation experiments suggest that antigen presenting cells play an important role. Finally, our views on reactive arthritis in the 1990s, and areas of new and potentially fruitful future research are presented.

Regulation of major histocompatibility gene expression in human vascular smooth muscle cells.

Human atheromata, but not normal blood vessels, contain numerous smooth muscle cells (SMC) that bear class II major histocompatibility (MHC) antigens. These lesions also contain leukocytes that can secrete cytokines, which may modulate SMC functions. Because of morphologic evidence for immune-activated (class II+) SMC in vascular lesions, we studied the regulation by cytokines of MHC gene expression in SMC cultured from human vessels. Under basal conditions, these SMC contained mRNA for class I MHC (detected by Northern blotting with a cDNA probe for HLA-B7) and expressed surface class I MHC product determined by enzyme-linked immunoassay with monoclonal antibody (MAb) W6/32. Unstimulated SMC contained little or no class II MHC mRNA (probed with HLA-DR alpha cDNA) or surface antigen (examined using MAb I2). Secretory products of activated human leukocytes (the cell-free supernatant of a mixed leukocyte reaction) induced class II MHC antigen expression by SMC after 3 days. Treatment of SMC with interferon (IFN)-alpha or -beta (1000 U/ml for 72 hours) increased class I MHC mRNA content and surface antigen but did not alter class II expression. Immune IFN (IFN-gamma), a leukocyte product known to induce class II MHC expression in classical antigen presenting cells as well as epithelial and endothelial cells, not only increased class I MHC expression by SMC but also induced substantial levels of class II MHC mRNA and surface antigen. IFN-gamma (ED50 approximately 10 U/ml) increased class II MHC mRNA maximally after 2 to 3 days and surface expression linearly from 1 to 4 days. Immunohistochemical study demonstrated few class II+ SMC in cultured human SMC under basal conditions but homogeneous expression of high levels of DR antigen after exposure to IFN-gamma for 3 days. Neither interleukin-1 (IL-1 alpha or beta), tumor necrosis factor alpha (TNF), nor endotoxin altered class II expression by SMC. Local secretion of IFN-gamma by activated leukocytes may account for the presence of HLA-DR+ SMC in the human atheroma. Immune activation of SMC might participate in the pathogenesis of vasculitis and arteriosclerosis, particularly in the form found in the coronary arteries of transplanted hearts.

Antigen Presenting Cells in Liver Biopsies from Patientsl with Primary Biliary Cirrhosis

Although Langerhans, interdigitating and follicular dendritic cells have been occasionally identified in pathological human liver by ultrastructural morphology, no data are available on their phenotypical their phenotypical identification using monoclonal antibodies. Frozen normal liver samples and biopsies from patients with primary biliary cirrhosis, primary sclerosing cholangitis and chronic active hepatitis were studied using a panel of 12 monoclonal antibodies (including anti class II antigens, follicular dendritic, macrophage and Langerhans cells). In normal liver, class II positive cells were represented by Kupffer and portal tract histiocytes with a macrophage phenotype. In pathological portal tracts non lymphocytic class II positive cells were represented by macrophages, clusters of follicular dendritic cells (which were detected in close association with B cell aggregates), and by sparse Langerhans cells (localized in areas of piecemeal necrosis and in a periductal position or infiltrating class II positive bile ducts). The present data suggest that both classical antigen presenting cells and class II positive bile duct cells may play some role in the induction of autoimmune reactions.

Adherent cells from rheumatoid synovia: identity of HLA-DR positive stellate cells.

Rheumatoid synovia were enzymatically digested and the in vitro morphology of different types of plastic adherent cells was observed. Four main types of cells were found after 24 hours in culture: stellate cells which had nuclei resembling those of classical cultured fibroblasts, but which stained positively with I2 antibody (anti-HLA-DR antibody); fibroblastic cells; cells which resembled morphologically in vitro macrophages and which were I2 and OKM-1 positive; round monocytes. The stellate cells did not stain with anti-S-100 or OKT-6 antibodies, which are used to detect classical antigen presenting dendritic cells. Furthermore, in the presence of indomethacin the stellate shaped cells were replaced by new I2 positive cells with a typical fibroblast shape. These results support the view that the stellate cells in synovial cell cultures represent HLA-DR positive fibroblasts, probably B cells of synovial lining.

Class II positive human dermal fibroblasts restimulate cloned allospecific T cells but fail to stimulate primary allogeneic lymphoproliferation

Recently, a number of laboratories have shown that gamma interferon (IFN-γ) is a potent modulator of HLA class II antigen expression in a variety of cell types ranging from classical antigen presenting cells to those not expected to participate in physiological antigen presentation such as fibroblasts. In order to examine the role of HLA class II expressing fibroblasts in antigen presentation, we established dermal fibroblast (FIB) strains from five HLA typed donors. After optimal preculture with IFN-γ, class II positive FIB were fully competent to restimulate proliferative responses of two DR specific T cell clones and one DP specific T cell line. However, they failed to elicit strong primary allogeneic proliferation from fully DR mismatched fresh PBMC. This failure was not due to a direct suppressive effect of FIB and could not be corrected by exogenous IL1 or by factors contained in conventional mixed leukocyte culture supernatants.