Immunological responses of cross-bred and inbred miniature pigs to swine poxvirus

Swine poxvirus (SPV), topically and subdermally applied to skin of the inguinal region of cross-bred and in-bred miniature pigs, caused typical pox lesions to occur with a pustular stage at 4 to 5 days p.i., and healing by 10 to 14 days p.i. Following inoculation, peripheral blood lymphocytes (PBLs) of the pigs showed lower transformation responses to SPV and mitogens (Concanavalin A, phytohemagglutinin and 12-0-tetradecanoly-phorbol 13-acetate) than PBLs from uninoculated controls. The PBLs generally responded to SPV from 7 to 9 days p.i. to 23 to 30 days p.i. with a maximum transformation response at the 12 to 13 days p.i. interval. Sera from the animals generally showed presence of SPV-neutralizing antibody as early as 7 days p.i. and a peak titer at 20 days p.i. of 1:512. No detectable SPV-antibody was observed at 50 days p.i. By 51Cr release assays, PBLs displayed the ability to lyse target cells in the presence of SPV-antibody with peak lysis from the 11th through the 21st day p.i. An antibody-histocompatibility restricted cell lysis was observed at 11 and 14 days p.i. When PBLs were depleted of adherent cells, there was a reduction in lysis of target cells indicating the adherent cells were instrumental as effector cells in the presence of SPV-antibody. Control pigs not exposed to SPV showed no PBL response to SPV-antigen. Partially histocompatible and non-histocompatible porcine kidney cells were found useful as cell models for evaluating SPV-infected pigs in their effort to immunologically respond to SPV.