CD79A and Recurrent upper respiratory tract infections: Using OmpC protein, BSA-linear peptide conjugate and BSA-cyclic peptide conjugate as antigens in an ELISA assay, the levels of IgA and IgG class anti-OmpC antibodies were determined in the sera of healthy donors, patients with humoral primary immunodeficiencies (PID) and patients with recurrent upper respiratory tract infections (RRTI).