MHC class II engagement inhibits CD99-induced apoptosis and up-regulation of T cell receptor and MHC molecules in human thymocytes and T cell line

AbstractMajor histocompatibility complex (MHC) class II surface levels on thymocytes increase after CD99 ligation. The functional implication of the up-regulated MHC class II was assessed by engaging MHC class II on CD99-ligated cells. MHC class II engagement down-modulated surface levels of T cell receptor and MHC molecules, and inhibited apoptosis of CD99-ligated thymocytes and CEM tumor cells, antagonistic effects on the previously reported CD99 functions. The results were reproducible regardless of the order of ligation of MHC class II and CD99. We suggest that signaling via MHC class II on CD99-engaged cells might be involved in the thymic maturation process by damping CD99 ligation effects

Delayed-Type hypersensitivity to latex: Computational prediction of MHC class II epitopes on latex allergens

Delayed type hypersensitivity to natural rubber latex is rare compared to IgE mediated immediate reactions. Binding of allergens to MHC Class II is a crucial step in the presentation of antigens to CD4+ T Cells responsible for delayed reactions. Computational prediction of MHC class II epitopes on thirteen known latex allergens using SMM-align method revealed strong binding with several alleles. This shows that latex allergens are capable of initiating delayed type hypersensitivity in susceptible individuals.
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The formation of immunogenic major histocompatibility complex class II-peptide ligands in lysosomal compartments of dendritic cells is regulated by inflammatory stimuli

During their final differentiation or maturation, dendritic cells (DCs) redistribute their major histocompatibility complex (MHC) class II products from intracellular compartments to the plasma membrane. Using cells arrested in the immature state, we now find that DCs also regulate the initial intracellular formation of immunogenic MHC class II-peptide complexes. Immature DCs internalize the protein antigen, hen egg lysozyme (HEL), into late endosomes and lysosomes rich in MHC class II molecules. There, despite extensive colocalization of HEL protein and MHC class II products, MHC class II-peptide complexes do not form unless the DCs are exposed to inflammatory mediators such as tumor necrosis factor α, CD40 ligand, or lipoplolysaccharide. The control of T cell receptor (TCR) ligand formation was observed using the C4H3 monoclonal antibody to detect MHC class II-HEL peptide complexes by flow cytometry and confocal microscopy, and with HEL-specific 3A9 transgenic T cells to detect downregulation of the TCR upon MHC-peptide encounter. Even the binding of preprocessed HEL peptide to MHC class II is blocked in immature DCs, including the formation of C4H3 epitope in MHC class II compartments, suggesting an arrest to antigen presentation at the peptide-loading step, rather than an enhanced degradation of MHC class II-peptide complexes at the cell surface, as described in previous work. Therefore, the capacity of late endosomes and lysosomes to produce MHC class II-peptide complexes can be strictly controlled during DC differentiation, helping to coordinate antigen acquisition and inflammatory stimuli with formation of TCR ligands. The increased ability of maturing DCs to load MHC class II molecules with antigenic cargo contributes to the \u3e100-fold enhancement of the subsequent primary immune response observed when immature and mature DCs are compared as immune adjuvants in culture and in mice

Rapid changes in shape and number of MHC class II expressing cells in rat airways after Mycoplasma pulmonis infection

This article is made available for unrestricted research re-use and secondary analysis in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.Mycoplasma pulmonis infection in rodents causes a chronic inflammatory airway disease with a strong immunological component, leading to mucosal remodeling and angiogenesis. We sought to determine the effect of this infection on the shape and number of dendritic cells and other major histocompatibility complex (MHC) class II expressing cells in the airway mucosa of Wistar rats. Changes in the shape of subepithelial OX6 (anti-MHC class II)-immunoreactive cells were evident in the tracheal mucosa 2 days after intranasal inoculation with M. pulmonis. By 1 week, the shape of the cells had changed from stellate to rounded (mean shape index increased from 0.42 to 0.77). The number of OX6-positive cells was increased 6-fold at 1 week and 16-fold at 4 weeks. Coincident with these changes, many columnar epithelial cells developed OX6 immunoreactivity, which was still present at 4 weeks. We conclude that M. pulmonis infection creates a potent immunologic stimulus that augments and transforms the OX6-immunoreactive cell population in the airways by changing the functional state of airway dendritic cells, initiating an influx of MHC class II expressing cells, and activating expression of MHC class II molecules by airway epithelial cells

MHC antigens in interferon γ (IFNγ) receptor deficient mice: IFNγ-independent up-regulation of MHC class II in renal tubules

MHC antigens in interferon γ (IFNγ) receptor deficient mice: IFNγ-independent up-regulation of MHC class II in renal tubules. MHC class II gene products in parenchymal cells, such as tubular epithelial cells in kidney, may play a role in the regulation of autoimmune reactions. Expression of MHC class II in renal tubular cells is normally very low, but it increases considerably under various pathologic conditions. The predominant role of IFNγ in up-regulation of MHC class II expression has been demonstrated repeatedly. We tested the existence of alternative pathways of MHC class II regulation using IFNγ receptor-deficient (IFNγR-/-) mice. Mutant and wild type mice received 50 µg bacterial endotoxin (LPS) i.p. Four days later the kidneys were removed for immunofluorescence examination. In agreement with published results LPS provoked an increase of immunoreactivity for MHC class I and MHC class II in proximal tubules of wild type mice. While MHC class I up-regulation was strictly IFNγ receptor-dependent, up-regulation of MHC II was still evident in mutant mice, although less than in wild type mice. Since injection of IFNγ induced proximal tubular MHC class II expression in wild type mice but not in IFNγR-/- mice, an alternative signaling pathway for IFNγ does not seem to exist. Thus, up-regulation of MHC class II expression in renal tubules does not necessarily require IFNγ. The markedly patchy pattern of immunofluorescence in IFNγR-/- mice suggests that induction of MHC class II after LPS injection may represent renal injury due to shock

Functional early endosomes are required for maturation of major histocompatibility complex class II molecules in human B lymphoblastoid cells

Major histocompatibility complex (MHC) class II molecules are targeted together with their invariant chain (Ii) chaperone from the secretory pathway to the endocytic pathway. Within the endosome/lysosome system, Ii must be degraded to enable peptide capture by MHC class II molecules. It remains controversial exactly which route or routes MHC class II/Ii complexes take to reach the sites of Ii processing and peptide loading. We have asked whether early endosomes are required for successful maturation of MHC class II molecules by using an in situ peroxidase/diaminobenzidine compartment ablation technique. Cells whose early endosomes were selectively ablated using transferrin-horseradish peroxidase conjugates fail to mature their newly synthesized MHC class II molecules. We show that whereas transport of secretory Ig through the secretory pathway is virtually normal in the ablated cells, newly synthesized MHC class II/Ii complexes never reach compartments capable of processing Ii. These results strongly suggest that the transport of the bulk of newly synthesized MHC class II molecules through early endosomes is obligatory and that direct input into later endosomes/lysosomes does not take place.</p

Roles of the Ubiquitin-Proteasome System and Mono-ubiquitination in Regulating MHC class II Transcription

Major Histocompatibility Complex (MHC) class II molecules are indispensable arms of the im-mune system that present extracellular antigens to CD4+T cells and initiate the adaptive immune response. MHC class II expression requires recruitment of a master regulator, the class II trans-activator (CIITA). How this master transcriptional regulator is recruited, stabilized and degraded is unknown. The 26S proteasome, a master regulator of protein degradation, is a multi-subunit complex composed of a 20S core particle capped on one or both ends by 19S regulatory particles. Previous findings have linked CIITA and MHC class II transcription to the ubiquitin proteasome system (UPS) as mono-ubiquitination of CIITA increases its transactivity whereas poly-ubiquitination targets CIITA for degradation. Increasing evidence indicates individual ATPase subunits of the 19S regulator play non-proteolytic roles in transcriptional regulation and histone modification. Our initial observations indicate proteasome inhibition decreases CIITA transac-tivity and MHC class II expression without affecting CIITA expression levels. Following cyto-kine stimulation, the 19S ATPase Sug1 associates with CIITA and with the MHC class II enhan-ceosome complex. Absence of Sug1 reduces promoter recruitment of CIITA and proteasome inhibition fails to restore CIITA binding, indicating Sug1 is required for CIITA mediated MHC class II expression. Furthermore, we identify a novel N-terminal 19S ATPase binding domain (ABD) within CIITA. The ABD of CIITA lies within the Proline/Serine/Threonine (P/S/T) re-gion of CIITA and encompasses a majority of the CIITA degron sequence. Absence of the ABD increases CIITA half-life, but blocks MHC class II surface expression, indicating that CIITA requires interaction with the 19S ATPases for both its deployment and destruction. Finally, we identify three degron proximal lysine residues, lysines (K): K315, K330 and K333, and a phosphorylation site, serine (S), S280, located within the CIITA degron, that regulate CIITA ubiquitination, stability and MHC class II expression. These are the first lysine residues identified as sites of CIITA ubiquitination that are essential for MHC class II expression. These observations increase our understanding of the role of the UPS in modulating CIITA mediated MHC class II transcription and will facilitate the development of novel therapies involving manipulation of MHC class II gene expression

Expression of RAB4B, a protein governing endocytic recycling, is co-regulated with MHC class II genes

The small GTPase RAB4 regulates endocytic recycling, a process that contributes to Major Histocompatibility Complex (MHC)-mediated antigen presentation by specialized antigen presenting cells (APC) of the immune system. The gene encoding the RAB4B isoform of RAB4 was singled out by two complementary genome-wide screens. One of these consisted of a computer scan to identify genes containing characteristic MHC class II-related regulatory sequences. The second was the use of chromatin immunoprecipitation coupled to microarrays (ChIP-on-chip) to identify novel targets of a transcriptional co-activator called the MHC class II transactivator (CIITA). We show that the RAB4B gene is regulated by a typical MHC class II-like enhancer that is controlled directly by both CIITA and the multiprotein transcription factor complex known as the MHC class II enhanceosome. RAB4B expression is thus activated by the same regulatory machinery that is known to be essential for the expression of MHC class II genes. This molecular link between the transcriptional activation of RAB4B and MHC class II genes implies that APC boost their antigen presentation capacity by increasing RAB4-mediated endocytic recycling

Mice lacking the MHC class II transactivator (CIITA) show tissue-specific impairment of MHC class II expression

CIITA activates the expression of multiple genes involved in antigen presentation and it is believed to be required for both constitutive and IFN\xce\xb3-inducible expression of these genes. To understand the role of CIITA in vivo, we have used gene targeting to generate mice that lack CIITA. CIITA-deficient (-/-) mice do not express conventional MHC class II molecules on the surface of splenic B cells and dendritic cells. In addition, macrophages resident in the peritoneal cavity do not express MHC class II molecules upon IFN\xce\xb3 stimulation nor do somatic tissues of mice injected with IFN\xce\xb3, in contrast with wild-type mice. The levels of li and H-2M gene transcripts are substantially decreased but not absent in CIITA (-/-) mice. The transcription of nonconventional MHC class II genes is, however, not affected by CIITA deficiency. A subset of thymic epithelial cells express MHC class II molecules. Nonetheless, very few mature CD4 T cells are present in the periphery of CIITA (-/-) mice despite MHC class II expression in the thymus. Consequently, CIITA (-/-) mice are impaired in T-dependent antigen responses and MHC class II-mediated allogeneic reponses