MOLECULAR-CLONING AND MESSENGER-RNA EXPRESSION OF PORCINE INTERLEUKIN-12

Interleukin (IL)-12 is a heterodimeric cytokine consisting of 35 and 4 0 kDa subunits, produced primarily by phagocytic cells in response to bacteria or bacterial products. IL-12 is important in the regulation o f both innate and antigen-specific immunity through its stimulatory ef fects on NK cells and cytotoxic lymphocytes. Reverse transcriptase-pol ymerase chain reaction with primers derived from human sequence was us ed to clone the p35 and p40 subunits of porcine IL-12. Predicted amino acid sequences for both subunits are approximately 85% homologous to their human cognates but contain a 3 aa addition and a 4 aa deletion i n p35 and p40 subunits, respectively. The high degree of similarity in dicates the proteins may be cross reactive, an important consideration in pig-human xenotransplantation. Both subunits of pIL-12 are constit utively expressed in a variety of porcine tissues. Highest levels of t he p40 subunit were found in lymphoid tissues including inguinal and m esenteric lymph nodes, Peyer's patches, spleen and thymus. The p35 sub unit was also detected in these tissues. Levels of mRNA encoding the p 40 subunit, but not the p35 subunit, were rapidly increased in alveola r macrophages stimulated with lipopolysaccharide or killed Staphylococ cus aureus. Thus, the heterodimeric subunits appear to be differential ly regulated at the transcriptional level. Since p40 also self-associa tes to form inactive homodimers, differential expression may be a mech anism for regulating IL-12 activity. (C) 1997 Elsevier Science B.V.