Studies on lymphocytes. V. Short in vivo DNA synthesis and generation time of lymphoid cells in the calf thoracic duct after simulated or effective extracorporeal irradiation of circulating blood

A dioestrous increase in thymocyte proliferation during the oestrous cycle

Coitus, which precedes internal fertilisation, is a unique physiological event which allows motile allogeneic spermatozoa to enter the female host and invade her tissues. The cyclic cellular proliferation observed in the thymus of the female rat may be an important preparation of her immune system for this event.

Proliferative kinetics of large and small intraepithelial lymphocytes in the small intestine of the mouse

The proliferative kinetics of the intraepithelial lymphocytes (IL) of the mouse intestine have been evaluated. By inducing mitotic arrest it was found that large IL - constituting about 50% of the IL - showed a mitotic rate of 2.3. Autoradiographic results obtained after two different schedules of 3H-thymidine injections showed that 30% of the large IL were in DNA synthesis, and that the large IL were renewed at a rate comparable to that of blast cells from Peyer's patches, mesenteric lymph nodes and thoracic duct lymph. The small IL were renewed very rapidly compared to small lymphocytes of peripheral lymphoid tissues, although small lymphocytes with lifespans of several weeks were also present in the epithelial sheet. By the use of intestinal perfusion, in vivo, it was estimated that the loss of lymphocytes from intestinal villi into the lumen of the gut was negligible, and it is concluded that the most probable kinetic model for the majority of IL is: B and T lymphoblasts invade the epithelium and undergo mitosis. B lymphoblasts give rise predominantly to plasma cells, and T lymphoblasts give rise to small lymphocytes - probably long-lived - which reenter the circulation.

The rate of division of antibody-forming cells during the early primary immune response

Mitotic blocking agents, colchicine or Velban, were used to estimate cycle times of spleen cells which release hemolysin for sheep erythrocytes (plaque-forming cells). The cells were obtained either from rats immunized with sheep erythrocytes or from cultures of mouse spleen cells immunized in vitro with the same antigen. 2, 3, or 4 days after immunization, animals or cell cultures were treated with mitotic blocking agents for periods of time ranging from 2.5 to 7 hr; plaque-forming cells were then enumerated. Decreased numbers of plaque-forming cells were found after such treatment. The extent of reduction was a function of duration of the drug treatment and the method of immunization, but was independent of the time after immunization. The evidence presented is consistent with premises that: (a) plaque-forming cells in mitosis do not release sufficient antibody to be detected, (b) mitotic blocking agents, by arresting plaque-forming cells in metaphase, prevent not only detection of these cells but also the increase in number of plaque-forming cells which would have resulted from cell division, (c) mitotic blocking agents do not affect release of antibody by cells in interphase. Cell cycle times, based on the extent of reduction of plaque-forming cells per unit time of drug treatment, were estimated using a mathematical model appropriate for an exponentially increasing population of cells. Cell cycle times estimated using the mitotic blocking agents agreed well with cell doubling times calculated from the increase in plaque-forming cells occurring 1-4 days after immunization. Increased responses produced by higher antigen doses or treatment of immunized animals with an adjuvant resulted from an increased rate of division of responding cells and their progeny. The results are consistent with a cell selection theory of antibody formation. Antigenic stimulation causes relatively few cells to proliferate and to synthesize antibody; apparently the magnitude of the response is dependent primarily on the rate of division of responding cells. It is suggested on the basis of observations of in vitro-immunized cell cultures that the rate of division of responding cells may be dependent on the rate of interaction between two cell types, both of which are essential for the in vitro plaque-forming cell response.