A panel of spontaneous BALB/c B cell lymphoma lines with different cell surface phenotypes were used to study the relationship of Fc receptors, Ia and Mls-associated (tentatively called LyM) antigens. These cultured lymphomas have the following B cell characteristics: They (a) express surface Ig; (b) have Fc receptors tested by sheep erythrocyte-antibody rosetting assay; (c) do not ingest latex particles, and (d) are negative for esterase activity.

One of these cell lines, A-20, is Ia+, Fc+, LyM+; another, M 12, is Ia-, Fc+, LyM+. Using these and other lines, we have shown that Fc receptors on Ia+ cells (e.g. A-20) can be inhibited by anti-Ia sera. There is no such inhibition on Ia- cells (e.g. M 12). However, anti-Mls serum can inhibit Fc rosetting on tumors with either Ia+ or Ia- phenotype.

Thus we can demonstrate inhibition of Fc receptors with anti-Ia sera similar to that reported for normal spleen cells.

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