To search for potential variants of SLA DOB

To search for potential variants of SLA-DOB and CD4 associated with different (percentage) levels of the five (T-lymphocyte subsets, total antibody IgG, interferon alpha (IFN-α), Toll like receptor 3 (TLR3), interleukin 6 (IL-6) in serum and porcine reproductive and respiratory syndrome virus (PRRSV)-specific antibodies) immune traits mentioned above in pregnant sows, we identified the variants of SLA-DOB and CD4 in pregnant Landrace sows through association analyses. These results provide important information for revealing molecular basis of immune traits, which can be used in molecular breeding for disease resistance of pregnant sows.
Methods
Results Descriptive statistical analysis was conducted on eight T-lymphocyte subsets, IFN-α, TLR3, IL-6, IgG, and PRRSV-specific b catenin inhibitor in 358 pregnant Landrace sows (Table 1). The 13 immune traits were plotted with probability distribution. Except for CD3−CD4+CD8−%, CD3−CD4+CD8+%, IFN-α, and IL-6, the other nine immune traits followed a normal distribution (Fig. 1), which were then used for subsequent association analysis.
Discussion Immunity at the early stage of pregnancy in human and other mammals is relatively low (Chaouat et al., 1999; Chaouat et al., 2004; Christiansen, 2013). The same phenomenon is observed in pregnant sows, whose lymphocyte conversion rate is significantly lower than that of non-pregnant sows (Zhang et al., 1982). The immunity of pregnant sows is closely related to disease resistance and fecundity. In this study, the genetic mutations in porcine SLA-DOB and CD4 genes and their associations with T-lymphocyte subsets, cytokines, and antibodies were analyzed using 358 pregnant Landrace sows. We detected twelve genetic mutations. In particular, eight of these mutations were located on the regulation and exon regions of the two genes, in which five variants were associated with immune traits (P < 0.05) except for SNP1, SNP3, and SNP10. Our results indicate that the five genetic mutations in SLA-DOB and CD4 can provide important basic data to improve the immunity traits of pregnant sows. Lymphocytes are a subgroup of leukocytes, and T and B lymphocytes mediate cellular and humoral immunity, respectively. Th cells, also known as CD4+T cells, and Tc cells, also known as CD8+T cells, are two important T lymphocytes that play important roles in cellular immunity. In this study, results of single-marker and haplotype association analyses show that the variants in SLA-DOB and CD4 genes are associated with the percentages of CD4+ T cells and/or CD8+T cells in T lymphocytes of pregnant sows, indicating that SLA-DOB and CD4 can be used as candidate genes for cell-mediated immunity in pregnant sows. Antibodies, also known as Igs, are the main components of humoral immunity. Our results showed that SLA-DOB and CD4 mutations and haplotypes are significantly associated with IgG and/or PRRSV-specific antibodies in pregnant sows. Thus, SLA-DOB and CD4 can also be used as candidate genes for humoral immunity in pregnant sows. Together, these variants in SLA-DOB and CD4 can serve as molecular markers for immunity improvement of pregnant sows. SNP2 of the SLA-DOB gene and the variants in the CD4 gene are associated with Th and Tc cells. SNP2 is associated with four important immune traits (CD3+CD4+CD8−%, CD3+CD4−CD8+%, IgG, and PRRSV-specific antibody). Ins9 in the CD4 gene, a type of four-base insertion mutation, and its homozygous inserted genotype (EE genotype) show a significant association with CD3+CD4+CD8−%, CD3+CD4+CD8+%, and PRRSV-specific antibody. This phenomenon may be explained by the connection between the two types of T cells, as Th cells can activate Tc cells. Thus, SNP2 and Ins9 could be a powerfully potential immune-related molecular marker for pregnant sows and is warranted for further functional tests. The CD4+/CD8+ T cells measure the ratio between Th cells and Tc cells. For healthy adult humans and mice, the CD4+/CD8+ ratio is about 2:1 in the peripheral blood (Winer et al., 2009). An inverted CD4+/CD8+ ratio indicates an impaired immune system. Patients with tuberculosis show a reduced CD4+/CD8+ ratio (Luz Correa et al., 2014). A decreased CD4+/CD8+ ratio is associated with aging and reduced resistance to infection and is an indicator of immunosenescence (Serrano-Villar et al., 2014; Yin et al., 2015). Compared with other mammals, the immune system of pigs show many unique changes (Binns et al., 1992; Joling et al., 1994; Saalmuller and Bryant, 1994), including an inverted lymphatic structure and medulla located outside of the cortex (Zuckermann et al., 2007; Lough et al., 2018). Normally, CD4−CD8− and CD4+CD8+ T lymphocytes mainly exist in the thymus of mammals, and they cannot be detected in the blood, except for pigs or at some extreme conditions (Bonomo et al., 1994; Jimenez et al., 2002; Wang et al., 2014a; Yu et al., 2015; Yang et al., 2018). In this study, the detection rates of CD4−CD8− or CD4+CD8+ T cells in the peripheral blood of pregnant sows were remarkably higher (27.9% and 11.0% for CD4−CD8− and CD4+CD8+ T cells, respectively), which are consistent with a previous study by (Wang et al., 2014a) in pigs. A low ratio of CD4+/CD8+ T cells has been observed in pigs (Huang, 1990). However, in this study, the ratio of CD4+/CD8+ T cells was relatively higher, which may be related to pig breeds, physiological period, and effects of PRRSV vaccine immunization.