A requirement for the Rho-family GTP exchange factor Vav in positive and negative selection of thymocytes.

The T cell repertoire is shaped by positive and negative selection of thymocytes that express low levels of T cell receptor (TCR) and both CD4 and CD8. TCR-mediated signals that determine these selection processes are only partly understood. Vav, a GDP-GTP exchange factor for Rho-family proteins, is tyrosine phosphorylated following TCR stimulation, suggesting that it may transduce TCR signals. We now demonstrate that mice lacking Vav are viable and display a profound defect in the positive selection of both class I- and class II-restricted T cells. In contrast, Vav is not essential for negative selection, though in its absence negative selection is much less effective. Vav may influence the efficiency of TCR-induced selection events by regulating the intracellular calcium flux of thymocytes.

Factors of nutritional health-seeking behaviors. Findings from the Georgia Centenarian Study.

Health-seeking behaviors are described by Harris and Guten (1979) as any behavior of an individual that promotes, protects, or maintains one's health, regardless of actual or perceived health status. The purpose of this study was to determine if nutritional health-seeking behavior (Bausell, 1986) comprised one or more factors for older adults (N = 256). Participants were in their 60s (n = 90), 80s (n = 91), and 100+ (n = 75). Exploratory factor analysis indicated that nutritional health-seeking behavior items formed two factors: avoid (i.e., avoiding unhealthy nutritional behavior) and seek (i.e., attempting or seeking healthy nutritional behavior). Multiple regression analysis revealed that risk factors for poor nutritional health-seeking behaviors in older adults include advanced age, low economic resources, and male gender. Protective factors included in the personality factors of self-discipline, enthusiasm, sensitivity, and warmth.

Syk tyrosine kinase is required for the positive selection of immature B cells into the recirculating B cell pool.

The tyrosine kinase Syk has been implicated as a key signal transducer from the B cell antigen receptor (BCR). We show here that mutation of the Syk gene completely blocks the maturation of immature B cells into recirculating cells and stops their entry into B cell follicles. Furthermore, using radiation chimeras we demonstrate that this developmental block is due to the absence of Syk in the B cells themselves. Syk-deficient B cells are shown to have the life span of normal immature B cells. If this is extended by over-expression of Bcl-2, they accumulate in the T zone and red pulp of the spleen in increased numbers, but still fail to mature to become recirculating follicular B cells. Despite this defect in maturation, Syk-deficient B cells were seen to give rise to switched as well as nonswitched splenic plasma cells. Normally only a proportion of immature B cells is recruited into the recirculating pool. Our results suggest that Syk transduces a BCR signal that is absolutely required for the positive selection of immature B cells into the recirculating B cell pool.