Characterization and mitogenesis of feline lymphocyte populations

Feline lymphocyte populations from blood, spleen, lymph node, thymus and bone marrow were examined for the following markers: rosette formation with guinea pig erythrocytes (GPE-T cells); surface feline thymocyte antigen (T cells); surface immunoglobulin (B cells); cytoplasmic immunoglobulin (preB cells, plasma cells); receptors for the Fc portion of IgG (FcyR-positive T and B cells), and the third component of complement (CR-positive cells - primarily B cells). The blastogenic responses of feline lymphocytes from peripheral blood, spleen, lymph node (LN), thymus and marrow were investigated using the following mitogens: Escherichia coli lipopolysaccharide (LPS), dextran sulfate (DxS), concanavalin A (conA), phytohemagglutinin (PHA) and pokeweed mitogen (PWM). Feline T lymphocytes identified by rosette formation with GPE and surface thymocyte antigen were present in thymus, spleen, LN, blood and, rarely, in marrow. T cell subsets, but not B cell subsets, were differentiated according to mitogen activation. Cells responding to PHA were immature, nonrecirculating cells, which were most strongly activated in thymus [stimulation index (SI) = 12], lymph node (SI = 11) and spleen (SI = 6). PWM-responsive cells were relatively mature, recirculating lymphocytes of widespread distribution and blastogenesis was greater in spleen (SI = 36) and LN (SI = 29), followed by thymus (SI = 23) and blood (SI = 15). Con A was a potent mitogen for cells of spleen (SI = 113), blood (SI = 80) and LN (SI = 77), but not thymus (SI = 7), suggesting that the con-A-inducible cell was a mature, recirculating, postthymic cell. Optimal mitogenic response to the B cell mitogen, LPS, was dependent upon increased cell concentrations (3 x 10(5) versus 1 x 10(5) per microtiter well) and increased incubation time (5 days versus 3 days). Surface IgG- and IgM-bearing lymphocytes and CR-bearing cells from spleen and blood were stimulated preferentially. DxS was moderately mitogenic for CR-bearing lymphocytes in spleen (SI = 4), LN (SI = 3) and blood (SI = 3), but not marrow (SI = 1).