Major histocompatibility complex molecule expression in the human central nervous system: immunohistochemical analysis of 40 patients.

To determine factors affecting major histocompatibility complex (MHC) molecule expression in situ in the human central nervous system (CNS) cryostat tissue sections from 36 autopsies and four biopsies were stained by immunoperoxidase with antibodies to class I (HLA-alpha chain, beta-2 microglobulin), class II (HLA-DR, HLA-DQ) MHC, lymphocyte, and macrophage antigens and Factor VIII-related antigen (VIII-RA). Stained cells and vessels/mm2 were counted in gray and white matter of four CNS anatomic levels. Class I molecules were found on parenchymal and endothelial cells (approximately 50% of VIII-RA + vessels) but not neurons, and were more abundant in gray than white matter (p less than 0.02). Class I molecules were absent in infants, but in adults expression was unaffected by age, sex, postmortem interval, presence of CNS lesions, or systemic illnesses. Expression of HLA-alpha chain and beta-2 microglobulin were the same. Class II molecules were usually absent but were found on parenchymal and endothelial cells in older adults, most frequently in association with macrophage infiltrates and spinal cord tract degenerations, but not with systemic illnesses. Expression of HLA-DR was greater than that of HLA-DQ. In the human CNS, regulation regulation of expression of MHC molecules is complex, can be affected by age, regional anatomy, and by local or remote CNS lesions, and may influence patterns and degrees of T cell immune responses.