Use of fluorescein conjugated staphylococcal protein-A as a labeling agent for porcine lymphocytes.

Staphylococcal Protein-A conjugated to fluorescein (FPA) was compared to a fluorescein conjugated sheep immunoglobulin anti-pig IgG (FSAPG) as a labeling agent for surface IgG positive (sIg+) porcine lymphoid cells. At plateau concentration of the reagents, more lymphoid cells were labeled with FPA than with FSAPG. However, on a protein concentration basis, FPA was less sensitive than FSAPG. As a control, FPA proved to be a poor labeling agent for sIg+ bovine lymphoid cells when compared to FITC conjugated rabbit IgG anti-bovine IgG (FRABG). Adsorptions of porcine lymphoid cells onto Protein-A Sepharose were performed in order to study the differential specificity of the Protein-A for sIg and for free immunoglobulins. The results of such absorptions showed that Protein-A Sepharose, whatever its affinity for Fab fragments from porcine immunoglobulins, could be used to enrich the sIg negative lymphoid cell populations in the pig.