Incidence of cells simultaneously secreting IgM and IgG antibody to sheep erythrocytes

The open carboxymethylcellulose (CMC) hemolytic plague technique has been used to study the question of whether plaque-forming cells (PFC) exist which can secrete both IgM and IgG antibody. Using a micromanipulation transfer technique, PFC were exposed serially to three types of plaque-revealing monolayers. One of these revealed chiefly IgM plaques; the second chiefly IgG plaques, and the third achieved discrimination between the true IgM-IgG double producers and certain atypical categories of PFC.Preliminary work was done to study the efficiency of serial cell transfer. It was found that 93% of both IgM PFC and IgG (enhanced) PFC could form three plaques. In fact, most cells could be transferred successfully more frequently. IgM PFC could make up to 30 successive plaques and IgG PFC up to 10 successive plaques.Experiments involving 3 different monolayers (direct, anti-μ antibody-containing, and anti-γ antibody-containing) were performed to search for cells capable of (a) forming IgG antibody of sufficient hemolytic activity to produce a plaque without enhancing serum; (b) forming IgM antibody of such potency as to break through the inhibitory capacity of anti-μ reagents; (c) forming non-complement-fixing IgM. Cells of categories (a) and (b) were easily found and distinguished from each other. Cells of category (c) were not found by us.The serial transfer approach outlined above was next used with the modification that the anti-γ antibody-containing monolayer was replaced by one containing a serum mixture capable of inhibiting most IgM PFC and of enhancing IgG PFC. Cells capable of making plaques in both this “enhancing-inhibitory” monolayer and in a direct monolayer, but not in the category of “breakthrough IgM PFC” or “lytic IgG PFC” were considered as true double-producers of IgM and IgG. Of 900 selected antibody-forming cells examined in either the primary or the secondary response of mice to SRBC, 14 (1.5%) were double producers.The present status of the hypothesis of an IgM to IgG transition in expanding immunocyte clones is briefly considered.