THE ROLE OF CD8(-INFECTIONS(), CD57(+) CELLS IN HUMAN CYTOMEGALOVIRUSAND OTHER VIRAL)

Peripheral blood lymphocytes expressing CD8 and CD57 determinants are a small (1-15%) subset in healthy humans. CD8(+), CD57(+) peripheral b lood lymphocytes may be divided by the level of CD8 expression, into C D8(high)(+)(CD57(+)) T-cells and CD8(low)(+)(CD57(+)) natural killer ( NK) cells, CD8(high)(+)(CD57(+)) T-cell numbers are increased in human cytomegalovirus (HCMV)-seropositive subjects, and there is substantia l evidence that HCMV is integral in the development of this subset in health and disease. Furthermore, the CD8(high)(+)(CD57(+)) subset is c lonally derived, expressing a limited range of T-cell receptors, and a re therefore likely to have restricted antigen specificity. Functional ly, CD8+(low)(CD57(+)) cells exhibit NK activity; while CD8(high)(+)(C D57(+)) T-cells from healthy subjects mediate contact-dependent suppre ssion in several in vitro systems including: (i) pokeweed mitogen-indu ced proliferation and immunoglobulin synthesis, and (ii) generation of antiviral MRC-restricted cytoxic T-lymphocytes. This is distinct from the nonspecific, soluble factor-mediated suppression exhibited from a phenotypically similar subset in human immunodeficiency virus (HIV) a nd bone marrow transplant recipients. This suggests an important immun oregulatory, suppressive role for CD8(high)(+) (CD57(+)) T-cells that may be potentiated by HCMV and altered in diseases associated with hig her numbers of this subset including HIV, allograft recipients and rhe umatoid arthritis.