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We report the distribution of genes encoding 11 killer cell immunoglobulin-like receptors (KIR) and 2 CD94:NKG2 receptors, in 32 Caucasians, 67 Australian Aborigines and 59 Vietnamese. The inhibitory and the activating KIR genes were found at different frequency in the three populations. No correlation was found between the polymorphism of the KIR genes and the HLA specificities of the tested samples. The most significant KIR associations were 2DL2 with 2DS2; 2DL2 with 2DS3 and 3DL1 with 2DS4 in all three study groups. In Caucasians and Vietnamese 2DS2 was associated with 2DS3 and 2DS1with 3DS1. KIR 2DL1 was strongly associated with three other KIRs: 2DL3, 3DL1 and 2DS4 in Aborigines. The distribution of the KIR phenotypes was different in the three populations. The AA1 phenotype was frequent in Vietnamese (42.4%) and Caucasians (31.2%), but very rare in Aborigines (1.5%). In contrast, the BB7 phenotype was very common for Aborigines (22.4%) and was absent in the two other groups. Our data demonstrate that different associations and putative KIR haplotypes could be distinguished in different populations.

The expansion of the cytokine-producing CD56bright NK cell subset is a main feature of lymphocyte reconstitution after allogeneic hematopoietic stem cell transplantation (HSCT). We investigated phenotypes and functions of CD56bright and CD56dim NK subsets from 43 HLA-matched non-T cell-depleted HSCT donor-recipient pairs. The early expansion of CD56bright NK cells gradually declined in the posttransplant period but still persisted for at least 1 year and was characterized by the emergence of an unusual CD56brightCD16low subset with an intermediate maturation profile. The activating receptors NKG2D and NKp46, but also the inhibitory receptor NKG2A, were overexpressed compared with donor CD56bright populations. Recipient CD56bright NK cells produced higher amounts of IFN-γ than did their respective donors and were competent for degranulation. Intracellular perforin content was increased in CD56bright NK cells as well as in T cells compared with donors. IL-15, the levels of which were increased in the posttranplant period, is a major candidate to mediate these changes. IL-15 serum levels and intracellular T cell perforin were significantly higher in recipients with acute graft-vs-host disease. Altogether, CD56bright NK cells postallogeneic HSCT exhibit peculiar phenotypic and functional properties. Functional interactions between this subset and T cells may be important in shaping the immune response after HSCT.