Molecular Requirements for T Cell Recognition by a Major Histocompatibility Complex Class II–restricted T Cell Receptor: The Involvement of the Fourth Hypervariable Loop of the Vα Domain

The role of two central residues (K68, E69) of the fourth hypervariable loop of the Vα domain (HV4α) in antigen recognition by an MHC class II–restricted T cell receptor (TCR) has been analyzed. The TCR recognizes the NH2-terminal peptide of myelin basic protein (Ac1-11, acetylated at NH2 terminus) associated with the class II MHC molecule I-Au. Lysine 68 (K68) and glutamic acid 69 (E69) of HV4α have been mutated both individually and simultaneously to alanine (K68A, E69A). The responsiveness of transfectants bearing wild-type and mutated TCRs to Ac1-11–I-Au complexes has been analyzed in the presence and absence of expression of the coreceptor CD4. The data demonstrate that in the absence of CD4 expression, K68 plays a central role in antigen responsiveness. In contrast, the effect of mutating E69 to alanine is less marked. CD4 coexpression can partially compensate for the loss of activity of the K68A mutant transfectants, resulting in responses that, relative to those of the wild-type transfectants, are highly sensitive to anti-CD4 antibody blockade. The observations support models of T cell activation in which both the affinity of the TCR for cognate ligand and the involvement of coreceptors determine the outcome of the T cell–antigen-presenting cell interaction

Effects of fisheries closure size, age, and history of compliance on coral reef fish communities in the western Indian Ocean

The hypothesis that the history of management compliance (strong versus variable), closure size (0.3 to 28 km2), closure age (2 to 39 yr), and habitat/geographic variables influenced total fish biomass, the number of species, and the ratio of herbivores to carnivores in no-take areas was tested. Twenty existing closures across 6 countries in the western Indian Ocean were sampled during the same time period (2004 to 2007). Geographic location and closure attributes were weak to moderate predictors of these coral reef fish community variables for analyses of all closures. Strong interactions between fish community variables and levels of compliance indicated that high compliance sites largely drove the closure–fish community relationships. Variable or weak compliance and closures <1 km2 exhibited limited recovery of fish communities. The closure area–fish biomass data for strong-compliance closures indicates that biomass is stable above 5 km2. A mix of community-based, private, and national program closures were sampled, and, although low sample sizes within each of these management systems precludes conclusive analysis, none of these management systems was universally successful in terms of compliance or maximizing fish community variables