Capping of surface immunoglobulin on rabbit and mouse lymphocytes. I. Kinetics.

: The capping behaviour of surface immunoglobulin (sIg) on rabbit and mouse B lymphocytes was investigated in the direct immunofluorescence test. Rabbit B lymphocytes showed fewer caps than mouse lymphocytes. This was not due to a lower rate of cap formation, but to a smaller subpopulation of cells able to form caps. This subpopulation was age-dependent in rabbits; it increased from 25% of sIg positive cells at 2 to 3 months to 50% at 2 to 3 years of age. The capping rate was not significantly different in rabbits and C57B1 mice, but it was much higher in Swiss mice. Endocytosis did not occur at temperatures below 30 degrees C. In mouse B cells endocytosis occurred exclusively in the cap configuration. In rabbit B lymphocytes, on the other hand, two types of endocytosis were observed: first, a rather rapid endocytosis during the formation of the patch configuration, occurring on small lymphocytes, and second, a rather slow endocytosis during the cap configuration, occurring on large lymphocytes.