Brief report: twin boys with major histocompatibility complex class II deficiency but inducible immune responses

The different isotypes serve similar functions, and their expression on cells is regulated in coordinated fashion.1 MHC class II molecules are expressed on the surface of certain cells of the immune system, such as monocytes and macrophages, B cells, and dendritic cells, where they play an important part in the immune response.2 MHC class II deficiency is an autosomal recessive disease characterized by cellular and humoral immunodeficiency.3 Family studies show that the disease locus segregates independently of the MHC class II gene loci,4 so the defect is not in the MHC class II genes themselves. Since the disease is associated with a high rate of early mortality, bone marrow transplantation is considered the only possible treatment.3,11 We report the case of identical twin brothers with a defect in constitutive and inducible surface expression of MHC class II molecules on B cells, monocytes, and activated T cells. Methods The expression of surface-membrane antigens on peripheral-blood leukocytes, T cells activated with phytohemagglutinin, and mononuclear cells incubated for 48 hours in the presence of recombinant human interferon gamma (500 IU per milliliter; Genzyme, Cambridge, Mass.) was examined by flow cytometry (FACScan, Becton Dickinson, San Jose, Calif.) with the following monoclonal antibodies used in direct two-color immunofluorescence as specified by the manufacturer (Becton Dickinson): HLA-DR (L243), CD19 (Leu-12), CD3 (Leu-4), CD14 (Leu-M3), and CD25 (interleukin-2 receptor). [...]the infants had a normal antigen-specific T-cell response after vaccination with tetanus toxoid, and this response was completely inhibited by the addition of a monoclonal antibody specific for MHC class II. [...]the T-cell response to recall antigen was restricted to MHC class II.