ANTI-SMOOTH-MUSCLE ANTIBODY IN CLINICAL HUMAN AND EXPERIMENTAL ANIMALMYCOPLASMA-PNEUMONIAE INFECTION

Autoantibody formation is possibly integral to the development of non- respiratory manifestations of acute Mycoplasma pneumoniae infection, W e sought to confirm the occurrence of smooth muscle antibodies (SMA) i n humans with acute Myc. pneumoniae respiratory infection and furtherm ore to assess whether similar autoantibodies would develop in a hamste r model of respiratory infection. Paired sera from 21 patients with ac ute infection were assayed for SMA by immunofluorescence on mouse kidn ey/stomach substrates, The frequency of SMA was then determined for 52 paediatric patients with acute Myc. pneumoniae infection and 16 contr ols, and for sera from a hamster model of infection, Five of 21 paired sera had an increment in SMA between acute and convalescent specimens , At a screening dilution of 1:40, 18/52 infected and 0/16 controls ba d positive sera (P = 0.003); positive specimens demonstrated IgG rathe r than IgM SMA. In the hamster model of Myc. pneumoniae respiratory in fection, significant IgG SMA increases occurred in 7/19 infections but not in 11 controls (P = 0.02), Immunoblotting did not identify actin as the substrate for SMA. Smooth muscle antibody increases are found i n a significant minority of Myc. pneumoniae-infected humans and hamste rs, A role for SMA in the pathogenesis of Myc. pneumoniae infection re mains to be defined.