Differential expression of CD8 alpha and CD8 beta associated with MHC-restricted and non-MHC-restricted cytolytic effector cells.
The differential expression of the alpha and beta chains of the CD8 glycoprotein was examined in three functionally distinct cytolytic effector cell populations: (i) T cells (CD3+ CD56-), (ii) NK cells (CD56+ CD3-), and (iii) non-MHC-restricted T cells (CD56+ CD3+). Twenty-four percent of T cells were CD8+, and they consistently coexpressed both CD8 alpha and CD8 beta. Moreover, CD8+ T cells uniformly expressed high-density CD8 alpha. Forty percent of NK cells were CD8+ but the vast majority (approximately 75%) expressed only CD8 alpha without CD8 beta. In addition, CD8+ NK cells uniformly expressed low-density CD8 alpha. In comparison, 75% of non-MHC-restricted T lymphocytes were CD8+ but they displayed an intermediate phenotype: 60% coexpressed CD8 alpha and CD8 beta while 40% expressed only CD8 alpha. Within this population, CD8 alpha was expressed at high density, similar to that of T cells. Following IL-2 activation, enhancement of non-MHC-restricted cytotoxicity was not associated with any changes in either the quantitative or qualitative pattern of expression of CD8 alpha or CD8 beta by these cells. Addition of either anti-CD8 alpha or anti-CD8 beta mAb did not alter non-MHC-restricted cytotoxicity of either CD56+ CD3- or CD56+ CD3+ effector cells. However, within the CD56+ cell population, non-MHC-restricted cytotoxicity was almost entirely found within the CD8- and CD8 alpha + beta- populations, and both subsets displayed a similar level of killing. In contrast, CD8 alpha+ beta+ cells exhibited very little non-MHC-restricted cytotoxicity. Thus, the coexpression of CD8 alpha and CD8 beta in conjunction with the TCR/CD3 complex appears to characterize MHC restricted cells while the expression of CD8 alpha alone is associated with non-MHC-restricted cytotoxicity. Taken together, these findings suggest that neither CD8 alpha nor CD8 beta is involved in the initial phases of target cell binding or recognition during NK cell-mediated lysis. However, the selective expression of CD8 alpha by a large fraction of non-MHC-restricted effector cells suggests that this antigen may play a different functional role in this unique subset of cytolytic lymphocytes.
Baume
D M
DM
Division of Tumor Immunology, Dana-Farber Cancer Institute, Boston, Massachusetts.
Caligiuri
M A
MA
Manley
T J
TJ
Daley
J F
JF
Ritz
J
J
D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000032:analysis; D000945:Antigens, Differentiation, T-Lymphocyte / Q000032:analysis*; D000954:Antigens, Surface / Q000032:analysis; D016827:CD8 Antigens; D003602:Cytotoxicity, Immunologic / Q000276:immunology; D006801:Humans; D007376:Interleukin-2 / Q000502:physiology; D007694:Killer Cells, Natural / Q000276:immunology*; D046911:Macromolecular Substances; D008285:Major Histocompatibility Complex / Q000276:immunology*
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D000954:Antigens, Surface; D016827:CD8 Antigens; D007376:Interleukin-2; D046911:Macromolecular Substances