Human natural killer (NK) cells express an abundant level of 2B4 and CD2 on their surface. Their counter-receptors, CD48 and CD58, are also expressed on the NK cell surface, raising a question about the functional consequences of potential 2B4/CD48 and CD2/CD58 interactions. Using blocking antibodies specific to each receptor, we demonstrated that both 2B4/CD48 and CD2/CD58 interactions were essential for the development of NK effector functions: cytotoxicity and cytokine secretion. However, only 2B4/CD48, but not CD2/CD58, interactions were shown to be critical for the optimal NK cell proliferation in response to interleukin (IL)-2. IL-2-activated NK cells cultured in the absence of 2B4/CD48 or CD2/CD58 interactions were severely impaired for their ability to induce intracellular calcium mobilization and subsequent ERK activation upon tumor target exposure, suggesting that the early signaling pathway of NK receptors leading to impaired cytolysis and interferon (IFN)-γ secretion was inhibited. Nevertheless, these defects did not fully account for the reduced proliferation of NK cells in the absence of 2B4/CD48 interactions, because anti-CD2 or anti-CD58 monoclonal antibody (mAb)-treated NK cells, showing defective signaling and effector functions, displayed normal proliferation upon IL-2 stimulation. These results propose the signaling divergence between pathways leading to cell proliferation and cytotoxicity/cytokine release, which can be differentially regulated by 2B4 and CD2 during IL-2-driven NK cell activation. Collectively, these results reveal the importance of homotypic NK-to-NK cell cross-talk through 2B4/CD48 and CD2/CD58 pairs and further present their differential and overlapping roles in human NK cells.

Natural killer (NK) cell development relies on signals provided from the bone marrow (BM) microenvironment. It is thought that lymphotoxin (LT) α1β2 expressed by the NK cell lineage interacts with BM stromal cells to promote NK cell development. However, we now report that a small number of RORγt+ innate lymphoid cells (ILCs), and not CD3−NK1.1+ cells, express LT to drive NK development. Similar to LT−/− or RORγt−/− mice, the mice conditionally lacking LTα1β2 on RORγt+ ILCs experience a developmental arrest at the immature NK stages, between stages of NK development to the mature NK cell stage. This developmental block results in a functional deficiency in the clearance of NK-sensitive tumor cells. Reconstitution of Thy1+ ILCs from BM or purified RORγt+ ILCs from lamina propria lymphocytes into LT-deficient RORγt+ BM cultures rescues NK cell development. These data highlight a previously undiscovered role of RORγt+ ILCs for NK cell development and define LT from ILCs as an essential molecule for the stromal microenvironment supporting NK cell development.

Current therapy for visceral leishmaniasis (VL), compromised by drug resistance, toxicity, and high cost, demands for more effective, safer, and low-cost drugs. Artemisinin has been found to be an effectual drug alternative in experimental models of leishmaniasis. Comparative genome and transcriptome analysis of in vitro-adapted artesunate-resistant (K133AS-R) and -sensitive wild-type (K133WT) Leishmania donovani parasites was carried out using next-generation sequencing and single-color DNA microarray technology, respectively, to identify genes and interlinked pathways contributing to drug resistance. Whole-genome sequence analysis of K133WT vs. K133AS-R parasites revealed substantial variation among the two and identified 240 single nucleotide polymorphisms (SNPs), 237 insertion deletions (InDels), 616 copy number variations (CNVs) (377 deletions and 239 duplications), and trisomy of chromosome 12 in K133AS-R parasites. Transcriptome analysis revealed differential expression of 208 genes (fold change ≥ 2) in K133AS-R parasites. Functional categorization and analysis of modulated genes of interlinked pathways pointed out plausible adaptations in K133AS-R parasites, such as (i) a dependency on lipid and amino acid metabolism for generating energy, (ii) reduced DNA and protein synthesis leading to parasites in the quiescence state, and (iii) active drug efflux. The upregulated expression of cathepsin-L like protease, amastin-like surface protein, and amino acid transporter and downregulated expression of the gene encoding ABCG2, pteridine receptor, adenylatecyclase-type receptor, phosphoaceylglucosamine mutase, and certain hypothetical proteins are concordant with genomic alterations suggesting their potential role in drug resistance. The study provided an understanding of the molecular basis linked to artemisinin resistance in Leishmania parasites, which may be advantageous for safeguarding this drug for future use.

Murine natural killer (NK) cells can mediate specific rejection of bone marrow cell (BMC) allografts. Whereas positive recognition of aliogeneic MHC antigens forms the basis for T cell alloreactivity, it has been postulated that NK cells are reactive against targets that do not express certain self-encoded MHC class I antigens. Here, we study the Immunogenlclty of BMC grafts from two class I transgenlc mice, D8 (B6 mice with an H-2D^d transgene) and C3H.L^d (C3H mice with an H-2L^d transgene). D8 BMC grafts are acutely rejected by B6 but not D8 recipients. This suggests that antigenic motifs associated with the H-2D^d molecule are recognized. B6 mice depleted of their CD3+ but not NK1.1+ cells can still reject D8 BMC grafts. These data suggest that NK1.1+/CD3- cells recognize the H-2D^d derived antigenic motifs. Similarly, C3H.L^d BMC grafts are rejected by B6 × C3H F₁ but not B6 × C3H.L^d F₁ recipients. Thus, antigenic motifs associated with the H-2L^d molecule can also be recognized. Furthermore, expression of either H-2D^d or H-2L^d by the recipients renders them unable to reject D8 or C3H.L^d BMC grafts. Therefore, H-2D^d and H-2L^d molecules appear to express common antigenic motifs recognized by NK cells. Additional studies with B6.R4 (K^bI^bS^bD^r), an intra-H-2 recombinant mouse, indicated that a third class I molecule, possibly H-2D^r, also shared the common antigenic motifs with both H-2D^d and H-2L^d molecules. Thus, positive recognition of class I antigens by NK cells can occur. However, expression of some of these antigenic motifs appear to be negatively controlled by certain H-2^r genes as suggested by rejection of D8 and B6.R4 BMC grafts by D8 × B10.RIII F_d and B6.R4 × B10.RIII F₁ hybrids respectively.