Differential T-cell expression of LFA-1 in residents from Africa and Denmark. Description of the phenomenon and its possible basis.

All circulating T cells constitutively express the adhesion molecule leukocyte function-associated antigen 1 (LFA-1; CD11a/CD18) at either low or high surface density. In the present paper we have compared the expression of the LFA-1 alpha-chain CD11a on peripheral T cells obtained from indigenous Africans with permanent residence in Africa to T cells from indigenous Danes with permanent residence in Denmark. The Africans had a higher percentage of T cells with high CD11a expression than did Danish donors. The difference was evident in both the CD3-, CD4+, and CD8+ subsets. The difference did not appear to reflect a higher degree of peripheral T-cell activation in the African donors, as T-cell expression of the activation marker IL-2 receptor (CD25) was similar in the two groups. Furthermore, we observed no apparent correlation between CD3+ CD11a(hi) and CD3+ CD25+ values in individual donors. LFA-1 expression on T cells obtained from expatriate Africans with long-term residence in Denmark resembled that of Danish permanent residents more than that of Africans with permanent residence in Africa. In addition, T cells obtained from two expatriate Danes with long-term residence in rural Africa were phenotypically similar to those from African permanent residents. The data suggest that the observed difference is environmental rather than ethnic and may reflect the degree of exposure to infectious agents.