Deoxyribonucleic acid synthetic response of mouse lymphoid cells in microculture with T-lymphocyte-dependent mitogens

Various numbers of mouse thymus, lymph node, or spleen cells were cultured in serum-containing medium with concentrations of 0.06 to 64 mug. per ml. of concanavalin A (Con A), using our version of the microculture technique. Maximal DNA synthetic responses were obtained with 1.0 million thymocytes (highest number used) at 4 mug. per ml. of Con A and with 0.75 million lymph node cells or 0.5 million spleen cells at 1 mug. per ml. of Con A. At optimal Con A concentration the magnitudes of response of 0.25 million thymus, compared with the same number of lymph node cells, were very similar. However, the response of lymph node cells was superior to that of thymocytes when 0.5 million initial cells were used, whereas 1.0 million thymocytes gave a better response than did the same number of lymph node cells. Regardless of the cell concentration, a comparison of responses by the three different cell types with the same cell number showed that the Con A concentration-DNA synthetic response curve was broadest for spleen cells, narrow for thymus cells, and intermediate for lymph node cells. Results in replicate experiments were highly reproducible, and the data indicated that peak DNA synthetic responses were not directly proportional to cell number when certain numbers of cells were used; the actual proportionality of response to cell number varied with the cell type and the mitogen concentration. When examined throughout the culture period, concentrations of Con A which were above the optimal for stimulation of DNA synthesis resulted in significant decreases in the number of viable cells. Time course experiments with Con A (or phytohemagglutinin)-stimulated BALB/c spleen cells showed that the initiation of DNA synthesis occurred between 12 and 24 hours of culture, with peak levels of 3H-thymidine incorporation occurring during the 2nd and 3rd days of culture. The presence or absence of fetal calf serum had essentially no effect on the Con A- or phytohemagglutinin-stimulated DNA synthetic responses during the 3rd day of culture. These results demonstrate that detailed evaluation of culture variables and mitogen concentrations is required for the most meaningful use of mitogen-stimulated DNA synthesis as a parameter for comparing different lymphoid cell populations.

Specific and nonspecific antitumor immunity. I. Description of an in vitro assay based on inhibition of DNA synthesis in tumor cells

As in vitro assay of cell-mediated antitumor immunity based on the inhibition of tumor cell DNA synthesis (IDS) was devised. It was reasoned that both cytolytic and cytostatic antitumor effects could be measured in a quantitative yet generalized manner with this approach. By the use of microculture techniques and simplified methods for the determination of tritiated-thymidine incorporation by all cells in individual cultures, normal and immune effector (E) cell populations were compared in their ability to inhibit the DNA synthesis of a fixed initial number of various target tumor cells. Doubling dilutions of E cells were used to titrate the antitumor effects of normal and immune cells at many E/T (effector to target) ratios. Under conditions of alloimmunization, significant immunologically specific IDS effects could routinely be detected at an E/T ratio of less than 1 or 0.1:1, and under certain conditions at 1:100 or less. Results were highly reproducible with respect to the individual E cell donors, replicate cultures, and repeat experiments. The effects were proportional to visually determined cell destruction and independent of obvious culture artifacts. The IDS method was compared with the 51Cr release technique under various experimental conditions. The results demonstrated that decreases in E/T ratio and/or the addition of excess nonimmune cells to immune effector populations had a similar effect in both assays, which was to decrease the magnitude of the immune cell activity. Addition of excess normal cells reduced the activity of immune cells to a level below that of an equal number of immune cells tested at the same E/T ratio without added nonimmune cells. Both assays detected primarily a T lymphocyte-mediated lytic event when effectors generated by the described alloimmunizations were used. The IDS assay also detected a weak non-T-cell activity in anti-theta plus complement-treated alloimmune spleen. The possibility that this represented antibody-dependent cell-mediated cytotoxicity was raised by the finding that normal spleen ceels plus antitarget antibody had significant activity in the IDS system. The sensitivities of the two methods were compared and the potential of the IDS method was evaluated.

Specific and nonspecific antitumor immunity. II. Macrophage-mediated nonspecific effector activity induced by BCG and similar agents

The recently described inhibition of DNA synthesis (IDS) assay, which measures antitumor effector (E) cell function by the quantitation of decreases in tritiated thymidine incorporation of target tumor cells, was used to analyze the nonspecific effector activity of peritoneal exudate cells (PEC) from mice infected intraperitoneally with BCG. These PEC could inhibit growth of and then kill all tumor target (effector to target) cells tested at E/T ratios as low as 1:1. This activity was not due to alterations in media, nor could any activity be shown for cell-free supernatants prepared from active cells. The principal cell type mediating this effector function was the "activated" macrophage-no activity was found in lymphoid or polymorphonuclear leukocytes. Direct effector to target contact was necessary for the cytotoxic reaction. The time course of these effects and comparative 51Cr release data were reported. The removal of the adherent nonspecific effectors from PEC of mice immunized to both BCG and a specific syngeneic tumor revealed a specific cytotoxicity of the remaining lymphoid cells. These results indicated that nonspecific effector activity by "activated" macrophages induced by BCG infection could be a potent antitumor mechanism, at least in vitro, and the IDS assay provided an accurate, reproducible, and quantitative method for measurement of the function of such E cells.

Linkage of susceptibility to experimental allergic encephalomyelitis to the major histocompatibility locus in the rat

Experimental allergic encephalomyelitis (EAE) was induced in rats of various genotypes by injection of 10 microg guinea pig basic protein in complete Freund's adjuvant containing 100 microg H(37) RV M. tuberculosis. Histologically verified EAE was present in 20/20 Lewis, 17/17 (Lewis x BN)F(1), 9/9 Lewis backcross, and 21/42 BN backcross rats. Among the BN backcross animals, 25/42 were determined to carry the major histocompatibility type characteristic of the Lewis strain and 21 of these had EAE. Separate groups of Lewis, BN, and (Lewis x BN)F(1) rats were immunized as described and skin tested on day 13 with 10 microg guinea pig basic protein and rat S basic protein. Animals of each genotype had Arthus and delayed skin reactivity to both antigens. These data are compatible with the hypothesis that susceptibility to EAE in rats is controlled by an autosomal dominant gene linked to the major histocompatibility locus. It is proposed that this is an immune response gene, designated Ir-EAE, which controls T cell reactivity directed against a highly encephalitogenic portion of the basic protein molecule.

Genetic control of thymus-derived cell function. I. In vitro DNA synthetic response of normal mouse spleen cells stimulated by the mitogens concanavalin A and phytohemagglutinin

Concanavalin A- or phytohemagglutinin-stimulated DNA synthetic responses of 1 million normal mouse spleen cells in vitro were significantly different among various inbred strains. BALB/cJ (H-2(d)) responded better than C57BL/6J (H-2(b)) spleen cells, and the responses of C3H/HeJ or AKR/J (both H-2(k)) cells were intermediate. These responses, measured as the increment in thymidine-(3)H incorporation of mitogen-stimulated compared with unstimulated cultures, varied according to the number of cells cultured or the mitogen concentration. BALB/c spleens had the highest proportion of theta-positive cells, but no direct relationship between the proportion of theta-positive cells and the DNA synthetic response was observed. (BALB/cJ x C57BL/6)F(1) spleen cells responsed as well as BALB/c cells. Responses of spleen cells from (F(1) x C57BL/6) backcross littermates varied over a range equal to, or greater than, that of BALB/c and C57BL/6 cells. There was no correlation between H-2 specificity (H-2(bd) or H-2(bb)) or sex and the mitogen-stimulated DNA synthetic response of backcross animals. Con A- and PHA-stimulated responses of individual backcross animals were positively correlated with the level of thymidine-(8)H incorporation by unstimulated spleen cells. These results are consistent with autosomal dominant, non-H-2-linked, polygenic control of the mitogen-stimulated in vitro DNA synthetic response of mouse spleen cells.

A histochemical study of gut maturation

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Antibodies to acetylcholinesterase

A rabbit antiserum against commercially available Electrophorus electricus acetylcholinesterase has been prepared. Five precipitation bands were distinguished by immunoelectrophoresis, but only three of these contained demonstrable enzyme activity. In an in vitro system, activity of the commercial enzyme or of highly purified acetylcholinesterase was inhibited by 70-82 per cent after incubation with antiserum. Antibody specificity was demonstrated by the absence of serological cross reactions or enzyme inhibition with bovine erythrocyte acetylcholinesterase or horse serum cholinesterase.