Determination of lactogenic activity in the serum of the squirrel monkey (Saimiri boliviensis) using the Nb2 lymphoma bioassay.

Determination of squirrel monkey prolactin by immunoassay has been hampered by the lack of antiserum specific to prolactin from this species. As an alternate method, we have investigated whether the Nb2 lymphoma bioassay could be adapted for routine measurement of the lactogenic activity of samples of squirrel monkey serum. The growth of the Nb2 cells is absolutely dependent on the presence of lactogens in the culture medium. The cells were maintained in Fisher's medium supplemented with 10% horse serum, 10% fetal calf serum (FCS), and 10M β-mercaptoethanol. For each assay, the cells were plated at an initial density of 1 × 10 cells/ml in 22-mm 12-well dishes in the above medium, but devoid of FCS. Serum samples were heated to 56°C for 20 minutes to abolish the unusually high cytolytic complement activity of squirrel monkey serum and were incubated for 72 hours with Nb2 cells at serial dilutions from 1/40 to 1/2,560. Growth curves were generated with pooled samples of squirrel monkey serum, and the level of lactogenic activity was estimated using a calibration growth curve generated with known concentrations of purified rhesus monkey prolactin standard. We have found that the Nb2 lymphoma bioassay provides a sensitive and adaptable means for determination of lactogenic activity in the serum of the squirrel monkey.