Deficiency of HLA molecules
HLA class I deficiency is a rare disease with remarkable clinical and biological heterogenicity. The spectrum of possible manifestations extends from the complete absence of symptoms to life-threatening disease conditions. It is usually diagnosed when HLA class I serological typing is unsuccesful, flowcytometric studies then reveal a severe reduction in the cell surface expression of HLA class I molecules (90-99% reduction compared to normal cells). Isolated HLA class I deficiency, also termed “type I bare lymphocyte syndrome” , is not usually life threathening, in contrast to the more severe HLA class II deficiency and combined HLA class I and class II deficiencies. The symptoms present in the majority of the patients are rather unexpected, considering the role of HLA class I molecules in the presentation of viral peptides to cytotoxic T lymphocytes.