T lymphocyte heterogeneity in the rat. III. Autoreactive T cells are activated by B cells

Evidence has been presented to show that CD4+ autoreactive T cell lines (ATs)2 in the rat require periodic stimulation with syngeneic spleen cells for in vitro proliferation. This proliferation can be blocked by treatment of the stimulator (spleen) cells with mAb to Ia antigens. Although ATs are Ia+ and can activate the allogeneic MLR, they fail to be autostimulatory. Fractionation of the spleen cells revealed that ATs can be stimulated with B cells and not by macrophages, although the latter were efficient in several accessory cell functions, including antigen presentation, lectin-dependent T cell activation and allogenic MLR response. Moreover, B cells proliferated and differentiated in response to AT cells. These data are compatible with a model in which ATs respond to hitherto undetermined B cell membrane antigen(s) in association with MHC class II antigens. These results may have important implications in understanding autoimmune responses.     

The effect of collagen on the cyclic AMP content of embryonic somites.

Previous studies have demonstrated that collagen substrates stimulate in vitro somite chondrogenesis, and that agents that elevate intracellular cyclic AMP levels in hibit the ability of somites to respond to the inductive influence of collagen. In the present investigation, radiommunoassay was utilized to compare the cyclic AMP content of somite explants cultured on purified Type I collagen substrates with control explants cultured on Millipore filters. During the period of culture, the cyclic AMP content of collagen-treated explants is significantly lower than the cyclic AMP content of control explants. The cyclic AMP content of collagen-treated explants is 66% of control values as early as one hour following the initiation of culture, and the cyclic AMP content of collagen-treated explants remains lower than controls throughout the 3-day cultured period. The greatest difference in the cyclic AMP content of collagen-treated and control explants is observed at the seventeenth hour of culture, at which time the cyclic AMP content of collagen-treated explants is 56% of controls. These results combined with previous studies provides support for the hypothesis that collagen elicits a reduction in the cyclic AMP content of embroyic somites and that this reduction is necessary to trigger chondrogenic differentiation.     

Purification, composition, and structure of macrophage adhesion molecule

Macrophage adhesion molecule (MAM) is a surface heterodimer consisting of the trypsin- and plasmin-sensitive glycopeptide gp160 (MAM-alpha) and the glycopeptide gp93 (MAM-beta). MAM, which is the guinea pig analogue of Mo1 and Mac-1, was purified from detergent lysates of peritoneal neutrophils by lentil lectin chromatography and M2-antibody chromatography. The pure heterodimer molecule was dissociated by acidic conditions (pH 3.5), and MAM-alpha and MAM-beta were separated by M7-antibody chromatography. MAM-beta is an approximately 640 amino acid residue polypeptide with exceptionally high cysteine content. At 7.2 residues per 100 amino acids, Cys/2 of MAM-beta is more than 3 times the mean for 200 purified proteins. Reactivity with six beta-subunit-specific monoclonal antibodies recognizing at least four epitopes demonstrated that intrapeptide disulfide bonds are required to maintain the structure of MAM-beta. All six antibodies failed to react when MAM-beta was treated with reducing agents. MAM-beta is 18% carbohydrate; the major monosaccharides are mannose, N-acetylglucosamine, galactose, and sialic acid. MAM-beta is estimated to contain five to six N-linked carbohydrate units. MAM-alpha is an approximately 1100-residue polypeptide with lower Cys/2 content (2.0 residues per 100 amino acid residues). MAM-alpha is 21% carbohydrate. The major monosaccharides are mannose, N-acetylglucosamine, galactose, and sialic acid; the mannose content is higher in MAM-alpha than MAM-beta. MAM-alpha is estimated to contain 12 N-linked carbohydrate units.     

The distribution,life cycle and production of Leptophlebia vespertina (L.) (Ephemeroptera) in a lowland lake

Oak Mere, the water body studied, is a moderately productive base-poor lowland lake. It has zones of submerged marginal vegetation growing on sand at the south-west end and on peat at the north-east end. The distributions of L. vespertina and other macroinvertebrates are described in relation to these two distinct areas. Laboratory experiments on behaviour and survival are described in an attempt to explain the patterns of distribution. The seasonal distribution, variations in population density, spatial distribution variance in relation to mean density, life cycle, length-weight relationship, growth and biomass of L. vespertina are then described during two years at the sandy south-west end. The data are used to estimate annual production. Distribution, life cycle, growth and production are compared with populations in water bodies of lower conductivity in the British Isles and Scandinavia.