Ovine interleukin-2: partial purification and assay in normal sheep and sheep with ovine progressive pneumonia

Interleukin-2 (IL-2), a T cell derived lymphokine, acts in nonspecific hormone-like fashion to maintain proliferation of activated lymphocytes in vitro and is believed to play a key role in cell-mediated immune function in vivo. The parameters of induction and assay of factors with IL-2 activity were examined in a group of clinically normal sheep seronegative for antibodies to ovine progressive pneumonia virus (OPPV-). Supernatants from cultures of Concanavalin A (Con A) stimulated mononuclear leukocytes (ML) derived from peripheral blood and lymph nodes contained factors with the capacity to maintain continued proliferation in Con A stimulated lymphoblasts. This activity was localized by gel chromatography to fractions containing proteins of 17,000-20,000 daltons. In a group of sheep seropositive for antibodies to OPPV (OPPV+), decreased levels of IL-2 activity were found in ML culture supernatants derived from the posterior mediastinal lymph nodes of sheep with clinical and pathological evidence of OPP, when compared to OPPV+ sheep with no lesions and sheep with visceral caseous lymphadenitis. This decrease in IL-2 activity appeared not to be associated directly with levels of prostaglandin E2 in these supernatants. These findings may correlate with virus induced alterations in cell mediated immune function in lymphoproliferative lesions of OPP.