Efficient pork production is often disturbed by Mycoplasma pneumonia of swine (MPS),causing significant economic loss.Breeding diseaseresistant livestock would thus be beneficial.Two lines that are expected to be resistant to MPS have been developed in Japan;the Landrace line,which is genetically selected for reducing the incidence of pulmonary MPS lesions,and the Large White line,which is genetically selected for the high immune capacity of peripheral blood.