Natural killer (NK) cells contribute to control of HIV/SIV infection. We defined macaque NK-cell subsets based on expression of CD56 and CD16 and found their distribution to be highly disparate. CD16 ؉ NK cells predominated in peripheral blood, whereas most mucosal NK cells were CD56 ؉ , and lymph nodes contained both CD56 ؉ and CD16 ؊ CD56 ؊ (doublenegative [DN]) subsets. Functional profiles were also distinct among subsets-CD16 ؉ NK cells expressed high levels of cytolytic molecules, and CD56 ؉ NK cells were predominantly cytokine-secreting cells, whereas DN NK possessed both functions. In macaques chronically infected with SIV, circulating CD16 ؉ and DN NK cells were expanded in number and, although markers of cytoxicity increased, cytokine secretion decreased. Notably, CD56 ؉ NK cells in SIV-infected animals up-regulated perforin, granzyme B, and CD107a. In contrast, the lymph nodehoming molecules CD62 ligand (CD62L) and C-C chemokine receptor type 7 (CCR7), which are expressed primarily on CD56 ؉ and DN NK cells, were significantly down-regulated on NK cells from infected animals. These data demonstrate that SIV infection drives a shift in NK-cell function characterized by decreased cytokine production, expanded cytotoxicity, and trafficking away from secondary lymphoid organs, suggesting that the NK-cell repertoire is not only heterogeneous but also plastic. IntroductionSince their discovery in the 1970s, natural killer (NK) cells have been considered the major effector cells of the innate immune system because of their ability to kill virus-infected or neoplastic cells. Although NK cell-mediated killing does not require prior antigen sensitization, cell-to-cell contact between NK and target T cells occurs through a complex array of inhibitory and activating receptors. In humans, NK cells express both killer-cell immunoglobulin-like receptors (KIRs), which interact with major histocompatibility complex (MHC) class I molecules and can be either inhibitory or activating, and receptors belonging to the C-type lectin family such as natural killer group 2A (NKG2A), an inhibitory receptor that recognizes HLA-E and NKG2D, which recognizes the stress-induced ligands MHC class I chain-related gene A and B (MICA/MICB) and members of the ULBP family. 1 Human NK cells also express various natural cytotoxicity receptors including NKp46, NKp30, and NKp44, for which the ligands remain incompletely characterized. 2,3 However, increasing evidence suggests that the complexity of NK-cell function has been underappreciated and that in addition to cytolysis of aberrant T cells, NK cells also produce a wide array of cytokines, mediate tolerance to self-antigens, and regulate dendritic cell functions. 4 Most recently, murine studies have suggested that NK cells may even display characteristics of adaptive immune responses. 5 In humans, 2 primary phenotypically defined subsets of NK cells have been described, cytolytic CD56 dim CD16 ϩ and cytokinesecreting CD56 bright CD16 Ϫ subsets, of which the CD56 dim CD16 ϩ subset predomina...

Retroviral restriction factor TRIM5␣ exhibits a high degree of sequence variation among primate species. It has been proposed that this diversity is the cumulative result of ancient, lineagespecific episodes of positive selection. Here, we describe the contribution of within-species variation to the evolution of TRIM5␣. Sampling within two geographically distinct Old World monkey species revealed extensive polymorphism, including individual polymorphisms that predate speciation (shared polymorphism). In some instances, alleles were more closely related to orthologues of other species than to one another. Both silent and nonsynonymous changes clustered in two domains. Functional assays revealed consequences of polymorphism, including differential restriction of a small panel of retroviruses by very similar alleles. Together, these features indicate that the primate TRIM5␣ locus has evolved under balancing selection. Except for the MHC there are few, if any, examples of long-term balancing selection in primates. Our results suggest a complex evolutionary scenario, in which fixation of lineage-specific adaptations is superimposed on a subset of critical polymorphisms that predate speciation events and have been maintained by balancing selection for millions of years.HIV ͉ retrovirus ͉ restriction

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Generation of Siae ⌬ 2/ ⌬ 2 mice Exon 2 of the Siae gene is unique to Lse . An engineered inframe deletion of exon 2 in a murine Lse complementary DNA resulted in a protein that lacked esterase activity ( Fig. 1 A ). Genomic deletion of exon 2 was achieved as described in the Materials and methods ( Fig. 1 B ). After germline transmission, homozygous mutant mice were generated and were found to be viable. Truncated exon 2 -defi cient Siae mRNA could be detected in KO mice (Fig. S3, available at http://www .jem.org/cgi/content/full/jem.20081399/DC1). Cytosolic esterase mRNA continues to be transcribed in these mutant mice. We refer to these KO animals as Siae ⌬ 2/ ⌬ 2 mice.Enhanced B lymphocyte antigen receptor signaling in Siae ⌬ 2/ ⌬ 2 mice Because Siae has the potential to remove 9-O -acetyl residues from ␣ 2 -6-linked sialic acid containing Siglec ligands, we predicted that B cells from mice lacking this esterase might exhibit enhanced BCR signaling similar to that noted in CD22-null mice ( 13 -16 ). Mice were fi rst bred into the C57BL/6 background for 10 generations. B cells from WT and Siae ⌬ 2/ ⌬ 2 mice were gated on, and the accumulation of cytoplasmic calcium after ligation of the BCR was analyzed using fl ow cytometry. As seen in Fig. 2 , BCR cross-linking resulted in an accelerated and enhanced calcium fl ux. A similar result was seen when purifi ed splenic B cells from mutant and WT mice were analyzed (Fig. S4, available at http://www.jem.org/cgi/content/ full/jem.20081399/DC1). These data suggested that in the absence of functional Siae, BCR signal strength is markedly enhanced and that this alteration in signal strength is an intrinsic property of mutant B lymphocytes.Defective CD22 signaling and hyperacetylation of ␣ 2 -6-linked sialic acid moieties on Siae mutant B cells The defect in Siae could result in the increased acetylation of ␣ 2 -6-linked sialic acid on N -glycans in B cells and, thus, attenuate the ability of glycoproteins on B cells to ligate CD22 and generate inhibitory signals. We sought to examine if there was a defect in CD22 signaling in Siae ⌬ 2/ ⌬ 2 mice. After BCR cross-linking, CD22 was isolated by immunoprecipitation, and immunoprecipitates were examined for CD22 tyrosine phosphorylation and for associated SHP-1 using Western blot assays. As seen in Fig. 3 (left, experiment 1; and right, experiment 2), tyrosine phosphorylation of CD22 after BCR signaling was reduced in Siae ⌬ 2/ ⌬ 2 mice in spite of similar levels of surface CD22 expression in WT and mutant mice ( It remained to be demonstrated whether a defect in Siae would result in enhanced 9-O-acetylation of ␣ 2 -6-linked sialic acid in Siae ⌬ 2/ ⌬ 2 mice. 9-O -acetylation of sialic acid has not