Attempts to demonstrate cell-mediated immune response during Mycoplasma suipneumoniae infection of pigs

Measurements of lymphocyte transformation and skin sensitivity were used to investigate whether pigs previously inoculated with Mycoplasma suipneumoniae would show a T-lymphocyte-mediated immune response. In the lymphocyte transformation test blood lymphocytes, obtained at various intervals after intranasal inoculation of M suipneumoniae cultures, were incubated with specific antigen and the degree of transformation was assessed by 14C-thymidine uptake. Reaction to intradermal antigen was assessed both grossly and histologically. Significant lymphocyte transformation was first obtained at approximately 15 weeks and was demonstrable up to the maximum observation period of 44 weeks after inoculation; this corresponded to the stage of progressive recovery from infection earlier described. Skin hypersensitivity, characterised histologically by perivascular mononuclear cell accumulation in the dermis, was demonstrated in all tests performed between 20 and 46 weeks after inoculation on previously infected pigs, and was apparently enhanced by repeated intranasal inoculation. Both types of responses were more marked in pigs inoculated with pathogenic M suipneumoniae than in pigs inoculated with attenuated M suipneumoniae.