Phenotypical and functional analysis of B lymphocytes of two siblings with combined immunodeficiency and defective expression of major histocompatibility complex (MHC) class II antigens on mononuclear cells.

Phenotypic and functional analysis of B lymphocytes in two siblings with combined immunodeficiency associated with defective expression of class I and class II major histocompatibility complex (MHC) antigens on mononuclear cells is described. The results of the analysis of the membrane phenotype of the B cells performed at the age of 1 and 5 years, respectively, by the use of monoclonal antibodies against class I (HLA-A, -B, -C) and class II (HLA-DR, -DP, -DQ) MHC antigens showed a decreased expression of class I antigens and a complete lack of class II antigens. Class I antigen expression consistently remained of the same magnitude during follow-up. Class II antigen expression remarkably had been positive early in life on B cells and activated T cells, whereas monocytes were negative for class II from birth onward. B lymphocytes of both patients responded in vitro to polyclonal activation with Staphylococcus aureus Cowan I staphylococci (SAC) with the production of IgM-type immunoglobulins only. This neonatal type of response was in agreement with the membrane immunoglobulin phenotype of the B cells since a high sIgM/sIgD ratio characteristic of neonatal B cells was present. However, the expression of the FMC7 antigen on B cells of both patients was comparable to that on B cells of normal adults. We hypothesized that the lack of MHC antigen expression may impose a resting state on the lymphocytes in these patients due to ineffective cellular interactions. In this view the high sIgM/sIgD ratio reflects the activation state of the B cells rather than the maturational state of the cells.(ABSTRACT TRUNCATED AT 250 WORDS)