The patients included in this study belong to a subset of common variable immunodeficiency (CVID) patients whose peripheral blood T cells have a T cell receptor (TCR)-mediated activation defect leading to impaired expression of the interleukin (IL)-2 gene upon stimulation with recall antigens (tetanus toxoid, Escherichia coli) or superantigens (staphylococcal enterotoxins). In the present report we demonstrate that the patients' peripheral blood T cells failed to generate the second messenger inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) following stimulation with superantigen or mAb specific for the monomorphic region of the TCR beta-chain. Patients' T cell lines were also impaired in generating Ins(1,4,5)P3 when stimulated with tetanus toxoid-pulsed autologous monocytes. Addition of a second or third co-stimulatory signal provided by recombinant IL-2, CD28 or both had no effect on the Ins(1,4,5)P3 formation of the patients' antigen-driven T cell lines. The T cell activation defect, however, was not absolute, as Ins(1,4,5)P3 formation in the patients' T cells after phytohemagglutinin or aluminium fluoride stimulation was normal. The impairment in signal transduction via the T cell antigen receptor was limited to the patients' T cells, as no activation defect after ligation of surface immunoglobulin, the antigen receptor on B cells, could be detected.

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...

Common variable immunodeficiency (CVID) is characterized by an impairment of specific antibody production and a decrease in all or selected Ig isotypes. Abnormalities at the level of the B cells, T cells, and antigen-presenting cells have been described. In the present study, we have focused our attention on T-cell activation in CVID. T cells from 15 of 24 patients failed to respond to recall antigens (eg, tetanus toxoid, Escherichia coli). Of these 15 patients, 11 were studied in detail and showed significantly decreased T-cell proliferative responses and/or decreased interleukin-2 and interferon- gamma production on T-cell receptor-mediated stimulation with recall antigens and superantigens (staphylococcal enterotoxins [SE]); however, T-cell response to mitogens (anti-CD3 monoclonal antibody, phytohemagglutinin) was normal. The defect in interleukin-2 and interferon-gamma release on tetanus toxoid stimulation could also be documented in purified CD4 T cells of the patients and was present in patients with high and normal CD8 counts alike. Furthermore, patients' T cells failed to mount a significant elevation in free intracellular calcium (Ca++ flux) in response to superantigen, whereas the response to phorbol myristate acetate and ionomycin, bypassing receptor-mediated signaling, was unimpaired. These results indicate a defect in the early phase of T-cell activation after triggering of the T-cell receptor in a significant subgroup of CVID patients.

SUMMARYCVID is a primary immunodeficiency syndrome comprising a heterogeneous group of patients with hypogammaglobulinaemia and defective formation of specific antibodies. Previous studies demonstrated defective T cell responsiveness to antigen in a major subgroup of patients. In the present study we investigated the capacity of peripheral blood monocytes and Epstein-Barr virus (EBV)-transformed B cell lines from seven patients with CVID, including two patients expressing an extended MHC haplotype described to be associated with CVID, to present antigen (Tet. Tox.) to CD4 þ antigen-specific T cell lines from healthy controls. The results presented show an unimpaired capacity of peripheral blood monocytes to present antigen in all patients studied. In addition, the present study demonstrates for the first time that CVID B cells function normally as antigen-presenting cells (APC). These findings indicate that expression of a certain MHC phenotype in CVID is not associated with a defect in the presentation of recall antigen by monocytes and B cells. Based on these studies, uptake, processing and re-expression of recall antigen in association with MHC class II molecules on the APC surface are functional and there is no indication for structural abnormalities of the MHC class II molecules expressed by the patients studied that could be essential for their function in antigen binding and presentation.

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