Sheep erythrocyte rosettes in pigs, sheep, cattle and goats demonstrated in the presence of dextran.

Formation of rosettes with sheep RBC by blood lymphocytes from young pigs was increased from 24.4% +/- 2.2 (mean +/- S.E.) in PBS to 54.1% +/- 1.9 in the presence of dextran. This increase was achieved without inducing appreciable rosette formation with other RBC which do not form rosettes in PBS. Lymphocytes which rosette only in dextran are predominant in pigs between 20 and 160 days old, when the peripheral lymphocyte pool is increasing very rapidly. The use of dextran revealed major populations of blood lymphocytes rosetting with SRBC in adult sheep (30.7% +/- 2.0), adult cattle (37.3% +/- 4.2) and adult goats (13.3% +/- 1.2). Proportions of rosette-forming lymphocytes tended to increase with age. In calf lymphoid tissues the distribution of rosette-forming lymphocytes suggested that these were T cells. In the improvement of rosette formation with SRBC, dextran was more effective than foetal calf serum, papain treatment of the SRBC or combinations of these treatments.