CD4 and contagious pleuropneumonia: There are several reports documenting an increased population of IL-17A producing T cells and secretion of IL-17A in pigs, such as the presence of Actinobacillus pleuropneumoniae specific Th17 cells [CD4+CD8αdimIL-17A+] in the blood and lungs of porcine contagious pleuropneumonia infected pigs (39).