Low dose X-irradiation of thymus filler cells in limiting dilution cultures of LPS-reactive B cells reduces the background Ig-secreting cells without affecting growth-supporting capacity.

Frequencies of lipopolysaccharide (LPS)-reactive B cells in the mouse can be determined in the limiting dilution culture system developed by Andersson et al. (1976, 1977a) which is completely dependent upon the presence of thymus filler cells, usually of rat origin. The assessment of B cell clones of mouse origin, however, can be hampered by the occurrence of varying numbers of thymus-derived immunoglobulin (Ig)-secreting cells. The number of these background Ig-secreting cells can be significantly reduced by low dose (110 mgray = 11 rad) X-irradiation of the rat thymus filler cells, without affecting their growth-supporting capacity.