Soluble factors in immune sera of mice. II. Reversible loss of surface immunoglobulin induced in vitro.

Serum collected from BALB/c mice at different time intervals during primary immunization induces in vitro a decrease of Ig+ cells in short-term cultures of normal spleen cells. The decrease was shown to be caused by loss of surface immunoglobulin (Ig) for the following reasons: no cell loss was detected which coulc account for it; the number of Ig+ cells returned to normal levels when the serum was removed and the cells were cultured further in fresh medium. The serum activity was recovered in a fraction with molecular weight less than 10,000 Daltons. The factor was active at 4 degrees C and on cells treated with high doses of Con A. Only a portion (25-30%) of the Ig+ cells are affected by this factor since after the initial decrease no further changes were observed during the 7 hr culture period. No changes in the distrubution of surface Ig was detected by fluorescent techniques on the remaining Ig+ cells. This factor was detected as early as 6 hr after immunization but its concentration was found 4-fold higher on the 7th day.