Natural killer (NK) cells are a group of innate immune cells that carry out continuous surveillance for the presence of virally infected or cancerous cells. The natural cytotoxicity receptor (NCR) NKp30 is critical for the elimination of a large group of tumor cell types. Although several ligands have been proposed for NKp30, the lack of a conserved structural feature among these ligands and their uncertain physiological relevance has contributed to confusion in the field and hampered a full understanding of the receptor. To gain insights into NKp30 ligand recognition, we have determined the crystal structure of the extracellular domain of human NKp30. The structure displays an I-type Ig-like fold structurally distinct from the other natural cytotoxicity receptors NKp44 and NKp46. Using cytolytic killing assays against a range of tumor cell lines and subsequent peptide epitope mapping of a NKp30 blocking antibody, we have identified a critical ligand binding region on NKp30 involving its F strand. Using different solution binding studies, we show that the N-terminal domain of B7-H6 is sufficient for NKp30 recognition. Mutations on NKp30 further confirm that residues in the vicinity of the F strand, including part of the C strand and the CD loop, affect binding to B7-H6. The structural comparison of NKp30 with CD28 family receptor and ligand complexes also supports the identified ligand binding site. This study provides insights into NKp30 ligand recognition and a framework for a potential family of unidentified ligands.

A once-daily regimen of emtricitabine, didanosine, and efavirenz proved to be safe and tolerable and demonstrated good immunologic and virologic efficacy in this 2-year study.

The lateral intercellular spaces (LIS) of reabsorptive epithelia are the site of the proposed local osmotic gradient responsible for transepithelial transport. We developed techniques for loading the LIS of living cultured renal cells (MDCK and LLC-PK1) with the fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF), visualizing LIS geometry, measuring pH, and determining the BCECF diffusion coefficient within the LIS. The LIS pH was remarkably constant and differed substantially from that of the superfusate in both the presence and absence of HCO3 or CO2. The LIS of MDCK cells had a pH of 7.66 +/- 0.04 in bicarbonate-free solutions of pH 7.0, 7.4, or 7.8. In bicarbonate-containing solutions, MDCK LIS pH was acidic to the superfusate by 0.3-0.4 units. In the absence of bicarbonate, the LIS of LLC-PK1 cells was markedly acidic (6.83 +/- 0.05), becoming alkaline by approximately 0.25 units in the presence of bicarbonate. Gradients in pH or dye concentration were not detected within the LIS. The diffusion coefficient of BCECF within the LIS was approximately equal to that seen in free solution.