Detection and characterization of a lymphocyte proliferating factor (LPF) in plasma of SJL/J mice infected with the LDH virus.

Infection of 25- to 30-week-old SJL/J mice with the lactate dehydrogenase (LDH) virus resulted in a transitory T-cell lymphocytopenia. However, in 40- to 45-week-old animals, the initial lymphocytopenia was followed by persistent elevations in the peripheral leukocyte counts (B and T lymphocytes). Studies indicated that this difference had its basis in a plasma factor, termed lymphocyte proliferating factor (LPF), which was induced by infection of older SJL/J mice with the LDH virus. Further experimentation revealed that plasma LPF was sensitive to storage at -60 degrees C, to heating at 90 degrees C, and to treatment with DNase. These results suggested an identification of LPF as DNA. This possibility was supported by the demonstration of LPF activity in association with DNA extracts (blood, spleen and lymph nodes from LDH virus-infected mice) which was inactivated by DNase.