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Cyclin D2 is the only D-type cyclin expressed in mature mouse B-lymphocytes, and its expression is associated with retinoblastoma protein (pRB) and pRB-related protein phosphorylation and induction of E2F activity, as B-cells enter the cell cycle following stimulation via surface IgM and/or CD40. Cyclin D-dependent kinase activity is required for cell proliferation, yet cyclin D2(-/-) mice have normal levels of mature B-lymphocytes. Here we show that B-lymphocytes from cyclin D2(-/-) mice can proliferate in response to anti-IgM and anti-CD40, but the time taken to enter S-phase is longer than for the corresponding cyclin D2(+/+) cells. This is due to the compensatory induction of cyclin D3, but not cyclin D1, which causes pRb phosphorylation on CDK4-specific sites. This is the first demonstration that loss of a D-type cyclin causes specific expression and functional compensation by another member of the family in vivo and provides a rationale for the presence of mature B-lymphocytes in cyclin D2(-/-) mice.

In this communication, evaluation of iron reserves was based on the estimation of mobilized iron from stores for hemoglobin synthesis in response to repeated phlebotomy.Thirteen healthy, hematologically normal, adult Indian prisoners from the local jail were selected for phlebotomy study. Whole blood equal to 10% of the red cell mass was withdrawn each week for 4 consecutive weeks. Hemoglobin, hematocrit, reticulocyte count, serum iron, and iron-binding capacity were estimated each week during the period of phlebotomy and the following 6 weeks.A small stress of removal of blood equivalent to 500–700 mg of iron resulted in decompensation and dieficiency in replacement of removed iron during the period of study in 5 of the 13 subjects. In another four subjects there was questionable evidence of decompensation. This study supports the concept that an iron-deficiency state may exist without manifest anemia, as all the individuals had normal hematological values to start with.

In this communication, evaluation of iron reserves was based on the estimation of mobilized iron from stores for hemoglobin synthesis in response to repeated phlebotomy.

1) Iron stores were quantitated histochemically in specimens of liver obtained from different geographical areas of the world with differing rates of prevalence of iron-deficiency anemia. A total of 1,586 specimens obtained from accidental deaths from India, Venezuela, South Africa, the United States, and the United Kingdom was studied. Another series of 1,672 liver specimens obtained from hospital deaths from Sweden, Czechoslovakia, the United States, and Venezuela was also studied separately.

1) Iron stores were quantitated histochemically in specimens of liver obtained from different geographical areas of the world with differing rates of prevalence of iron-deficiency anemia. A total of 1,586 specimens obtained from accidental deaths from India, Venezuela, South Africa, the United States, and the United Kingdom was studied. Another series of 1,672 liver specimens obtained from hospital deaths from Sweden, Czechoslovakia, the United States, and Venezuela was also studied separately.2) Sections were stained for hemosiderin and evaluated on an arbitrary system of grading from 0to V.3) The study revealed an extreme paucity of iron stores in some population groups—Indians, South African Indians, and Mexicans. Highest iron stores were found in South Africans, Bantus, and Whites. The iron stores for the United States, the United Kingdom, and Venezuela fell in between these two extremes. In general, the iron stores in the population studied seemed to be related to the magnitude of iron-deficiency anemia in that population insofar as it can be ascertained from published reports.4) The study has revealed that even in a well-developed country such as the United States in which frank iron-deficiency anemia is not a major problem, there is a substantial number of persons with extremely low iron stores, indicating their vulnerability to the development of anemia.5) The study has also shown that males have significantly higher iron stores than females in all groups studied.