Allogeneic antiserums against human lymphocytes were specifically inhibited by M protein from beta hemolytic group A Streptococcus pyogenes, type 1. Analogous M proteins from streptococcus types 3, 4, 5, 6, 12, and 14 had little or no inhibitory activity. The specific inhibition by M protein is not a result of anticomplementary activity or of coating of the lymphocyte surface. Streptococcal polysaccharide and 73 other polysaccharides were inactive. Because all seven HL-A specificities tested were inhibited, it is inferred that M1 protein has a structure common to human histocompatibility antigens.

Abstract. Light and electron microscopic features and immunohistochemical features of Cryptosporidium andersoni (C. andersoni) and host reaction in the mucosa were studied. Although the affected cattle demonstrated no apparent clinical signs, a severe infection of C. andersoni was observed in the abomasum. C. andersoni were round in shape, measured 6-8 mm in size and were mainly observed to be freely located in the gastric pits, being attached in occasional cases to the surface of the abomasum epithelium. Frequent inflammatory cells had infiltrated the lamina propria of the affected mucosa, and frequent mitotic figures were observed in epithelial cells at the dilated isthmus. To access the cell kinetics, the number of epithelial cells infected with C. andersoni were counted and compared with noninfected cattle. The number of gastric pit cells in infected cattle was significantly higher than that in the controls. The number of proliferative cells determined by the Ki-67 antigen in C. andersoni infected cattle was also significantly higher than that in the controls. Transmission electron microscopy and scanning electron microscopy revealed that the morphology of the C. andersoni organism was common to those of other Cryptosporidium spp. Immunohistochemically, several commercial antibodies against Cryptosporidium spp. showed positive reactions at the wall of these oocysts or parasitophorous vacuoles. This report is possibly the first to discuss the prominent hyperplasia of the abomasum mucosa, as well as morphologic features of C. andersoni in cattle.

Human lymphocytes sensitized with HL‐A antibodies could not be killed by the addition of complement if the lymphocytes were incubated for periods of 1 to 5 hours at 37° C. This phenomenon was not produced by simple dissociation of the antibodies or by loss of antigens (modulation), but rather is postulated to result from an active release or pinocytosis of HL‐A antigens together with the attached antibody. “Escape from sensitization” is followed closely by reformation of antigens, for the cells can readily be resensitized and killed by addition of complement. Loss of sensitization is an active process, since one‐day‐aged lymphocytes or lymphocytes treated with actinomycin D or puromycin were unable to express this activity. A differential escape rate for different specificities was encountered indicating that HL‐A9 was produced more rapidly than several other specificities present on the same lymphocytes. A correlation was noted between the rate of HL‐A antigen synthesis by lymphocytes (indicated by escape rate) and the quantity of HL‐A antigen in the serum. Inhibition of lymphocyte cytotoxicity was used to detect the presence of HL‐A antigens in serum. Certain specificities, such as HL‐A9, were generally present in serum whereas others, such as HL‐A8, could not be detected. Cross‐inhibition tests with over 100 sera clearly showed an association of inhibition with specificity, although nonspecific inhibition was often observed. Sephadex fractions of sera tested at different concentrations revealed the greatest inhibitory activity in the 19S and 7S fractions.

Antibodies which were cytotoxic to lymphocytes were found in patients with kidney transplants, Graves' disease, Hashimoto's disease, rheumatic heart disease, and in multiparous women. These cytotoxins were 19S, optimally reactive at 15° C, were autocytotoxic to lymphocytes, and were inactive against granulocytes. The specificity of their reactivity to allogeneic lymphocytes was unrelated to HL‐A specificities. In fact, though the sera varied from 1% to 99% in reactivity against a panel of random donors, much of the variation seems to be of a quantitative nature with relatively little specificity. Out of 6,105 x2 comparisons between 110 sera of the diseases mentioned above, 83% were positive and none of the negative x2 values were statistically significant. It is concluded that diverse stimuli elicit the formation of these low avidity 198 antibodies which are directed against a non‐HL‐A antigen richly represented on lymphocytes. Although their biologic significance may be difficult to show, as with cold hemagglutinins, they could possibly act as a “natural” antilymphocytic serum.

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