Titres of specific antibodies to poliovirus type 3 and tetanus toxoid in saliva and serum of children with recurrent upper respiratory tract infections

A study of antibody levels (in saliva and blood) against common vaccine antigens was performed in a population of 32 children suffering from recurrent upper respiratory tract infections (URTI). None of the patients had primary or secondary immunodeficiency syndromes or other known predisposing factors for respiratory diseases. Titres of the isotype‐specific antibodies immunoglobulin A (IgA), immunoglobulin M (IgM), and immunoglobulin G (IgG) against two vaccine antigens – poliovirus type 3 (P3) and tetanus toxoid (TT), a viral antigen and a bacterial antigen, respectively – were measured in unstimulated saliva and serum, both in patients and in 24 healthy children (controls), by using a standard enzyme‐linked immunosorbent assay (ELISA). In addition, levels of total IgA and avidity of IgA antibodies to both P3 and TT in saliva were evaluated. No difference was found between patients and controls as to levels of total IgA, or specific IgA and IgM antibodies against both P3 and TT in saliva. Furthermore, the avidity of salivary IgA antibodies against the two antigens did not differ between the two populations. However, the average concentrations of saliva‐specific IgG antibodies to both the viral and the bacterial antigen were significantly lower (p < 0.01 for P3 and p < 0.05 for TT, respectively) in saliva of children with recurrent URTI, whereas no difference was found in serum for any immunoglobulin isotype determined compared with healthy individuals. The results of the present study provide suggestive evidence for the existence of subtle IgG‐restricted defects in antibody responses at the mucosal level, but not at the serum level, in some children with undue susceptibility to URTI.