Ia antigen expression by human malignant lymphomas: correlation with conventional lymphoid markers

The Ia (p23,30) antigens are useful in determining the B- or T-cell origin of normal peripheral blood lymphocytes. However, exceptions to the preferential B-cell expression of Ia antigens exist, i.e., many plasma cells are Ia– and T cells are rarely Ia+. Therefore, we investigated Ia expression (assayed by direct immunofluorescence using heteroantisera) by cells isolated from 33 malignant lymphomas and 7 benign lymph nodes. This was compared with surface immunoglobulin (SIg) and sheep erythrocyte (SRBC) receptor (E rosette) expression. Results with normal lymph nodes were similar to those described for peripheral blood. Most lymph node B cells were Ia+SIg+. Occasional Ia+SIg– B cells and rare Ia+ T cells were present. Ia antigens were expressed in parallel with SIg in 15 of 19 B-cell lymphomas. In 4 B-cell lymphomas, substantial numbers of neoplastic Ia+SIg– cells were also present, suggesting the presence of neoplastic cells at varying stages of differentiation. Heterogeneity was also seen in those lymphomas associated with monoclonal proteins, as small numbers of Ia+ and Ia– plasma cells were present. Seven cases expressed the T-cell (la–SIg–E+) phenotype. The common acute lymphoblastic leukemia phenotype (Ia+SIg–E–) was rarely expressed and may be uncommon among lymphomas. Three lymphomas expressing the Ia+E+ phenotype were shown to be B-cell malignancies whose SIg had SRBC specificity. One Ia 4 T-cell lymphoproliferative disorder was found. Thus, Ia antigens are useful B-cell markers in most instances. Furthermore, their enumeration allows the demonstration of phenotype heterogeneity in B-cell malignancies, analogous to that described for T-cell malignancies.