Molecular characterization of major histocompatibility complex class II gene expression and demonstration of antigen-specific T cell response indicate a new phenotype in class II-deficient patients.

Abstract

StlmmaryMajor histocompatibility complex (MHC) class II deficiency is an inherited autosomal recessive combined immunodeficiency. The disease is known as bare lymphocyte syndrome (BLS). BLS is characterized by a lack of constitutive MHC class II expression on macrophages and B cells as well as a lack of induced MHC class II expression on cells other than professional antigenpresenting cells (APCs) due to the absence of mRNA and protein of the human leukocyte antigen (HLA) class II molecules, designated HLA-DR, -DO~ and -DP. The defect in gene expression is located at the transcriptional level and affects all class II genes simultaneously. Here we have analyzed transcription and protein expression of class II antigens in Epstein-Barr virus (EBV)-transformed B lymphoblastoid cell lines and mononuclear cells (MNCs) of twin brothers. Whereas flow cytometric analysis failed to detect class II antigens on the cell surface of the patients' EBV-B cells and MNCs, examination of the genes coding for HLA-DR, -DQ, -DP, and the invariant chain (Ii) by reverse transcriptase-polymerase chain reaction amplification resulted in an unusual mRNA pattern in the B cell lines of the patients (HLA-DRa § -DtLS-, -DQo~ +, -DQ~-, -DPol-, -DP~ +, Ii+). In accordance with these findings no HLA-DRB-specific protein was detected by immunoblotting, whereas low levels of HLA-DRo~ and normal levels of Ii were present. In contrast to EBV-B cells, the MNCs of both patients displayed a residual HLA-DILS, -DOff, and -DPol mRNA signal. Furthermore, HLA-DRB-specific protein was found in addition to HLA-DRc~ by immunoblotting of cell lysates, even though it was dearly decreased as compared with controls. Our results indicate that the defect in class II antigen expression is not necessarily present to the same extent in B cells and cells of other lineages, mRNA levels of HLA-DtL8 were found to be enriched in adherent cells within the MNC fraction. Further investigations indicated that the MHC class II expressed is functional in antigen presentation, as the two boys' CD4 + T cells became activated and expressed interleukin-2R after stimulation of peripheral blood mononuclear cell cultures with recall antigen (tetanus toxoid). Furthermore, T cells tested in one of the two patients responded to both MHC class I and II allostimulation, and this response was inhibited by monoclonal antibodies of the respective specificity. Whereas the MNC population contained sufficient APCs to activate CD4 + T cells in response to antigenic stimulation, the patients' EBV-B cells were unable to present recall antigen to autologous, long-term cultured, antigen-reactive T cells or to a normal, HLA-DR-compatible, antigen-specific T cell line. In contrast, the patients' EBV-B cells functioned normally as accessory cells for mitogen-induced T cell proliferation. The results obtained from the investigations of MHC class II-dependent immune functions indicate antigen presentation by a subset of cells, obviously present in the HLA-DtL8 mRNA-expressing adherent MNC population, where...

Mutation in the Class II trans-Activator Leading to a Mild Immunodeficiency

“…1e) and patient BCH (31). However, a milder immunodeficiency associated with a residual HLA class II expression has been described for the Ker/ Ken twins (14) and is shown here for a patient KhM from BLS group B (Fig. 1f).…”

“…MHC II-deficient patients with mild clinical presentation have previously been reported, e.g., the 7-year-old KER twins. Their T cells were able to respond in vivo to antigenic challenge (13,14). Although the molecular basis of the MHC II defect was not elucidated in these twins, the Sa patients do not share the same defects, because their cells complemented the KER cell line for MHC-II expression.…”

“…KER B cell lines (13,14) from the patients were also used. Phenotypic complementation was tested by immunofluorescence 48 -72 h after cell fusion.…”

Impaired Regulation of HLA-DR Expression in Human Immunodeficiency Virus-Infected Monocytes

“…One of the interesting features of our system is that there is a selective loss of mRNA for HLA-DR, while mRNAs for HLA-DM and Ii are transcribed. Although HLA-DR, HLA-DM, and Ii have been reported by some investigators to be transcribed coordinately (28), more recent studies have shown that HLA-DR and Ii genes are not always coordinately transcribed (21,31,89). The HLA-DR and Ii promoters differ in spacing between the X and Y boxes (85,86), and mutational analysis of HLA-DR and Ii promoters has demonstrated differences in the contribution of W/Z/S-box binding (23).…”

Specific complex formation between the type II bare lymphocyte syndrome-associated transactivators CIITA and RFX5

“…Recently, a potential fifth complementation group has been reported. The atypical phenotype of these latter patients exhibited discoordinate regulation between ␣ and ␤ chains and low levels of class II surface expression on some cell types (6,7). Transacting factors are responsible for these various defects since fusion of B cell lines derived from patients with those from a patient representing a different complementation group or with a normal cell line restores class II expression.…”