A maximal interline separation has been obtained after 10 consecutive generations of selective breeding for the character "quantitative in vitro response of lymph node lymphocytes to the mitogenic effect of phytohaemagglutinin". At the selection limit the difference between high and low responder lines was about 20-fold. A similar interline separation has been demonstrated for the T-mitogen effect of concanavalin A. The identical response to PPD (purified protein derivative of tuberculin), a B mitogen, proved that the genetic selection has only modified the potentialities of T lymphocytes. During the selective breeding, responsiveness to PHA stimulation has been always measured under identical culture conditions. To demonstrate that the interline difference in responsiveness was due essentially to genetic factors independent of environmental effects, a systematic study of various culture conditions has been undertaken. The optimal stimulation was found after two days of culture for high line cells and after three days for low line cells. The difference between maximal responses was only slightly lower than that obtained after a two-day culture as used for the selection test. Increase in cell concentrations produced higher thymidine incorporation. In the two lines, a linear correlation was established between the cell concentration and the response produced. The maximal response given by the highest number of low line lymphocytes was equivalent to that given by a number, 11-fold smaller, of high line cells. Within certain limits, changes in the amount of tritiated thymidine added to the culture did not affect the interline separation. With a thymidine of high specific activity, a sub-evaluation of uptake by high line cells decreased the interline difference. Results in mixed culture of lymph node cells from high and low lines indicated that the low response was not due to the release of inhibiting factors or to the presence of suppressive cells in low responder mice. In conclusion, separation of these two lines was due to genetic factors acting independently of the cell culture conditions.

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The cells involved in the modification of the in vitro immune response by Corynebacterium parvum (C. parvum).

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[Response to PHA of lymphocytes from two lines of mice genetically selected for "high" or "low" antibody synthesis (author's transl)].

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[Genetic selection of mice for quantitative responsiveness of lymphocytes to phytohemagglutinin].

A two-way selection was performed in mice according to the quantitative response of small lymphocytes to the mitogenic activity of phytohaemagglutinin (PHA). The response of inguinal lymph node cells of each mouse to an optimal dose of PHA was measured by 3H-thymidine incorporation using a micro-plate method. Starting from four outbred mouse strains we mated on the one hand mice getting the best response and on the other hand mice getting the poorest response. A progressive separation of the two lines was observed. At the 7th generation a 3-fold difference was found between the two lines. A similar interline difference was observed when concanavalin A (ConA) was used as mitogen. The separation of the two lines was also evident when spleen cells or thymus cells were cultured with PHA or ConA.

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