Sonia Baur

The proteins on surfaces of living splenic lymphocytes from normal BALB/c mice were iodinated enzymatically. Such cells were fractionated into two sub-populations: one composed almost exclusively of small lymphocytes and the other mainly of large lymphocytes and plasma cells. Specific immunoprecipitation of radiolabeled surface Ig obtained from lysates of these cell populations indicated that approximately 2-3% of the acid-precipitable radioactivity from the cell surface is Ig. Moreover, 95% of the H chain radioactivity from the Ig of the small lymphocyte fraction and 90% from the large lymphocyte-plasma cell fraction was characterized as micro by precipitation with anti-micro sera as well as by molecular weight determination on polyacrylamide gels in sodium dodecyl sulfate. The Ig was recovered from the cell surface in the form of an IgM monomer. Control experiments suggested that the monomer did not result from depolymerization of 19S IgM by the methods used to radiolabel and isolate the molecule. (3)H-tyrosine labeling of IgM produced by meyloma cells and radio-iodination of IgM in solution gave the same ratios of microL radioactivity as radiolabeling of IgM on cells, indicating that the tyrosine residues of L and micro-chains of cell surface IgM are available to the lactoperoxidase during the iodination. This is consistent with the hypothesis that cell surface IgM is entirely on the outside of the plasma membrane presumably attached to it by its Fc fragment. These results, together with previous reports by others, suggest that IgM, in its monomeric form, is the main antigen-specific receptor on lymphocytes of normal mice.

Discussion and Summary The experimental results indicate that lactoperoxidase-catalyzed iodination of viable lymphoid cells is limited to the plasma membrane. Radiolabeled molecules from the cell surfaces of myeloma, lymphoma and normal spleen cells can be specifically precipitated with anti-Ig sera. Reduction and alkylation of these precipitates yield H and L chains. Gamma chain is present on P3K cells and µ chain on Daudi cells, as expected. Mµ chain was the predominant H chain found on spleen cells, consistent with recent experiments of others using lymphocytes (5, 10, 13, 16). Ig on the surface was not adsorbed to the plasma membrane and therefore presumably was synthesized by the cells. These findings provide evidence that Ig molecules on the plasma membrane, whether antigen-specific receptors or molecules destined for secretion, can be isolated and studied by conventional methods of immunochemistry and biochemistry.

Leptin (L) is associated with body-weight-regulating and adipostatic functions. Its receptors also may be found centrally. Thyroid hormones regulate metabolic processes mainly by binding at peripheral receptors. Aim of this study was to show if there is a link between those central and peripheral regulation systems and to investigate the influence of different training intensities on L and the hypothalamic-thyroid-axis (HTA) in highly trained rowers. Six rowers (18.9 +/- 2.6 y; BMI 22.8 +/- 2.1 kg/m (2)) undertook high intensity resistance training (RT) for three weeks followed by three weeks of endurance training (ET). After each training cycle the subjects had one week for recovery (R1, R2). Blood samples were taken before and at the end of RT, R1, ET and R2. L, thyroid stimulating hormone (TSH), free T3 (fT3) and free T4 (fT4) were measured. After RT, a significant reduction in L, TSH and fT3 was found (p < 0.05). fT4 was unchanged. L remained decreased until the end of R1. After ET, a significant increase of TSH was found. L correlated to basal TSH levels (r = 0.49, p = 0.006) during R. BMI and body fat were unchanged throughout the study and were not correlated with hormonal levels. We speculate a high energy flux during intensified training (RT) caused the decrease of L and the HTA, independent of BMI or body fat. Thus, we conclude a depression of L and HTA is associated with training intensity.

The gastric parietal cell auto-antigen is localized essentially in the microsomal fraction of mucosal homogenates obtained by centrifugation over a sucrose density gradient. The fractionation is facilitated by digestion of gastric mucus with ficin before disruption of the tissue. The antigen was assayed by a quantitative complement-fixation method. The effect of a number of enzymes and chemical treatments upon the serological reactivity of a gastric microsomal preparation was studied. The properties of the gastric antigen suggest an intimate association with insoluble lipoprotein elements of the microsomal membranes. Although immunologically distinct and strictly organ specific, the cytoplasmic auto-antigens of the stomach, and of the thyroid gland, show a remarkable resemblance in their biochemical characteristics. This similarity has a parallel not only in the embryo-logical origin and the iodide trapping mechanisms which the two organs share in common but also in the close serological and clinical associations that have been demonstrated between auto-immune atrophic gastritis and thyroiditis.