The rate of capping and shedding of cross-linked surface immunoglobulins (SIg) was slower in old Lewis rats (greater than 24 mo) than in young Lewis rats (3-4 mo). Analysis of spleen cell populations with the fluorescence-activated cell sorter indicated that with aging there was a loss of cells with a high density of SIg. Cells with the highest density of SIg capped and shed cross-linked SIg faster than cells with a low density of SIg. The alteration in density of SIg may account for the difference in capping kinetics. Colchicine treatment increased the rate of capping of lymphocytes from young animals, but had no effect on the capping kinetics of lymphocytes from old animals.

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