Platelets, lymphocytes, and megakaryocytes, specifically processed for the intracellular detection of antigens, were studied by indirect immunofluorescence techniques using monospecific antibodies directed against factor VIII-related antigen (F-VIII-RA). Specific staining was observed in platelets of the peripheral blood from normal individuals and from patients with haemophilia A, and in megakaryocytes and platelets of bone marrow from normal subjects. The same cells studied in patients with von Willebrand’s disease were negative. No bone marrow biopsies were performed on patients with haemophilia A. Our results indicate that F-VIII-RA is localized in megakaryocytes and platelets of normal subjects; the possible role of this F-VIII-RA in platelet function is discussed.

Semiquantitative estimates of circulating endotoxin were performed by the limulus test in patients suffering from typhoid fever and other salmonelloses. The test was positive in a large number of cases. However, no clearcut correlation was found between existence of endotoxemia, as such, and pyrexia. A correlation with recent bacteremia was found for highest levels of endotoxin activity. In minor salmonelloses a striking prevalence of positive cases was observed in the age group under one year. These findings were discussed in relation to the diagnostic and pathogenetic facets of the problem.

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Data on the mitotic index of human granulocytopoietic cells are presented. From these and from the duration of mitosis directly measured in living cells by phase contrast microscope, the weighted average generation time and the mean compartment transit time are computed. Maturation in granulocytopoietic cells appears to induce a reduction of mitotic indices and mitotic rate and an increase in mitotic time and in mean compartment transit time. Part of the increment in mitotic duration may be due to the acquisition by a part of the granulocytopoietic cells of cytoplasmic peripheral motility or other specialized activities, thus distracting part of the energies destined to mitosis.

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The mitotic behavior of pernicious anemia and normal erythropoietic cells in vitro was studied by means of phase contrast microphotography and cinema-photograph. Direct measurements showed that the duration of mitosis is significantly shorter in megaloblasts than in normoblasts at every stage of maturation. Maturation induces an elongation of mitosis in both the normal and the pathologic series. The mitotic index being practically the same in normoblasts and megaloblasts, the weighted average generation time in megaloblasts, calculated according to the formula tG = tM/IM, resulted in a shorter time than in normoblasts. This indicates that there is a higher than normal proliferative activity of p.a. cells since the generation time appears inversely proportional to the frequency by which new mitoses are entered in a cell population. The role of each single mitotic phase in shortening the total duration of mitoses has been investigated. Possible alterations in the mitotic mechanisms involved have been discussed.

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