Functional evaluation of CD19- and CD22-negative variants of B-lymphoid cell lines

By co-cultivating lymphoid B-cell lines with ricin-A conjugates of CD19 and CD22 monoclonal antibodies, we generated cell line variants that selectively lacked CD19 or CD22 antigens. The expression of other B-cell antigens was not affected by the treatment. Loss of the CD19 antigen did not result in alterations in growth ability of the cells, while CD22-negative variants had an impaired colony formation ability, as detected by a sensitive clonogenic assay. Cell cycling properties of both CD19- and CD22-negative variant lines did not differ from those of parental lines. These results are in line with previous observations that correlate the presence of CD22 antigens on the membrane with the ability of B cells to proliferate. Besides inducing the loss of cell surface reactivity, CD22-ricin-A treatment induced also the loss of CD22 intracytoplasmic expression. The antigen-negative cell lines restored their original phenotype in 20-40 days after discontinuing co-cultivation with ricin-A conjugates. With the return of CD22 positivity, cells recovered their colony-formation ability. These results further underline the importance of CD22 in regulating the growth of B cells.