The relationship between the morphology of rosette-forming cells and their mode of rosette formation.

Rats were injected in the footpad with sheep erythrocytes. The proportion of each morphological type of rosette-forming cell in the popliteal lymph node was measured, , performing the immunocyto-adherence technique at 4° and 37°. Among the different morphological types of rosette-forming cell, which appear after immunization, few plasmacytes form rosettes at 4°. The number of rosettes formed at 37° was increased by the addition of anti-rat immunoglobulin (Ig) to aliquots of lymph node preparations from rats 7 days after immunization. This increase was accounted for by an increase in the number of rosette-forming plasmacytes and rosette-forming cells intermediate between small blasts and plasmacytes, and was thought to be due to the detection of cells secreting non-haemagglutinating antibody. The enhancing effect of anti-rat Ig at 37° contrasted with its inhibitory effect at 4°. The presence of 10 M puromycin only slightly reduced the number of rosettes as compared with untreated control aliquots, but it prevented or reduced the enhancing effect of anti-rat Ig. The addition of anti-rat Ig to aliquots of lymph node preparations from rats 4 days after immunization reduced the number of rosettes formed as compared with control aliquots. It is considered that plasmacytes lack a surface associated antigen-binding receptor and depend for their rosette-forming ability on the secretion of antibody.