IMMUNOLOGICAL COMPETENCE OF SMALL LYMPHOCYTES 24I 



Simonsen and co-workers (1958). To test for acquired tolerance, 

 single, full-thickness skin homografts were made from adult 

 C57BL/6 donors, employing the technique of Billingham and 

 Medawar (195 1). 



Results 



Characterization of the lymphocyte preparations 

 inoculated 



As indicated in the previous section, the final preparations 

 injected into neonatal mice were 96-100 per cent pure and 99-100 

 per cent viable with respect to lymphocytes. Since the problem of 

 lymphocyte purity was of paramount importance in these studies, 

 high cell yield was sacrificed to obtain pure preparations. With 

 many of the preparations injected, no monocytes or granulocytes 

 whatever were observed among hundreds of lymphocytes 

 counted on Wright-stained films. Nevertheless, not all of the 

 lymphocytes could confidently be classified as small lymphocytes 

 on the basis of morphology alone (see Fig. i). It was, therefore, 

 crucial to determine whether large or medium lymphocytes, 

 known to be capable of mitosis, were present in the preparations 

 injected. 



Several preparations of purified, peripheral blood lymphocytes 

 from C57BL/6 adults of both sexes were tested by the tritiated 

 thymidine-radioautographic technique previously described. 

 The film strips subsequently developed, after incubation of the 

 shdes for periods ranging from one week to six weeks, revealed 

 no uptake of labelled thymidine whatever among thousands of 

 lymphocytes counted. Hence, the supposition that our prepara- 

 tions contained no appreciable number of blood cells capable of 

 mitosis was confirmed, and the assumption that we were employ- 

 ing small, and not medium or large, lymphocytes was reinforced. 

 It might still be argued that these small lymphocytes, assumed to 

 be end cells, may divide after locahzation in certain tissues outside 



