Response of lymphocytes from pigs naturally infected with porcine respiratory disease complex at 3 different stages of development.

The objective of this study was to analyze the response of lymphocytes from pigs naturally infected with porcine respiratory disease complex (PRDC) at 3 different stages of development. Porcine respiratory disease complexes were isolated from 2 groups: The infected group, consisting of pigs with PRDC and no vaccination against any virus (n = 24), and the control group, consisting of vaccinated and noninfected piglets (n = 24). Both groups were sampled at 3 stages of development: Weaning (WEA) (n = 8), initiation (INI) (n = 8), and growth (GRO) (n = 8). The PRDC status was confirmed by serological testing against porcine circovirus type 2 (PCV-2), porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza virus (H1N1), and Mycoplasma hyopneumoniae. PCV-2+ cells were quantified by flow cytometry. Weight gain was registered at each stage. PCV-2+ cells, CD4+ cells, monocytes and lymphocytes populations were measured. Gene expression in CD4+ cells was quantified for interferon-γ (IFN-γ), GATA binding protein 3 (GATA3), T-box transcription factor (T-bet), interleukin-10 (IL-10), and IL-4. Control piglets gained approximately 35% more weight than those infected with PRDC. Specifically, PCV-2+ cells were detected in piglets from the infected group in the following proportions: WEA ≤ INI ≤ GRO. In infected piglets, the CD4+ count increased at WEA and decreased at GRO, CD4+ expression profile showed an overexpression of T-bet at INI and GRO, and the expression of IFN-γ was lower at WEA and GRO. In contrast, IL-4 was overexpressed at all 3 stages. GATA3 was overexpressed at INI and GRO. The infected piglets showed lymphopenia and less CD4+ cells. CD4+ cells showed a different expression profile than the control group, in which IFN-γ was less expressed, whereas IL-4 and T-bet were overexpressed.