Protection by natural infection and vaccination against respiratory diseases caused by mycoplasmas.

Following recovery from mycoplasmal respiratory disease animals are resistant to reinfection. The mechanism of this immunity is not well understood; usually there is poor correlation between circulating antibody levels and the degree of resistance to reinfection, but more work is needed to both man and animals on the significance of the different classes and types of circulating antibody. Because mycoplasmal infection of the respiratory tract is largely confined to the epithelial surface, it seems likely that local immunity will prove to be important. The levels of specific immunoglobulins, particularly IgA, in respiratory tract secretions may be related to immunity. It is probably, however, that cell-mediated immunity is the main determinant of resistance to mycoplasmal respiratory disease: firstly, there is evidence in several diseases that lymphocytes can be transformed by mycoplasmal antigen and there are some indications thatthe degree of this cell-mediated immunity might correlate with resistance to infection; secondly, antigen has produced skin reactions indicative of delayed hypersensitivity in some mycoplasmal diseases. Vaccination with inactivated vaccines has not produced satisfactory immunity; attenuated mycoplasma strains or temperature-sensitive mutants seem more likely to afford adequate protection against respiratory diseases caused by mycoplasmas.