Characterization of surface components of Moraxella catarrhalis and pathogenic Neisseria

Infection is a multistep process including adhesion, colonisation, invasion and multiplication which finally results in disease. Bacterial surface components and virulence factors are essential for all these different steps and they are co-ordinately regulated during the different steps of pathogenesis and infection. Host factors like the mucosal barrier, complement, phagocytosis, humoral and cellular immune response result in either elimination of pathogen or, if they fail to protect the body, progress of the disease process.

LPS is an indispensable surface component and important virulence factor of gram- negative bacteria. The antibody response against different LPS serotypes of M. catarrhalis was studied in hyperimmune rabbit sera and a predominant serotype specific antibody response was observed. On the other hand, in the human host, humoral immune response was mainly observed against the common inner core region of the LPS. Immunochemical characterization of LPS epitopes by monoclonal antibodies confirmed the presence of a Gal-alpha-(1-4)-Gal epitope in the LPS of M. catarrhalis which is in agreement with the chemical structure of M. catarrhalis LPS. The humoral immune response against major outer membrane proteins was also studied in paired sera from patients suffering from a respiratory tract infection caused by M. catarrhalis. Titre rise in specific IgG 1, IgG2 and IgG3 was observed in most of the patients. Optimal sensitivity was obtained by using the OMP as antigen and testing for a rise of IgG3 antibodies. A good correlation was observed between total immunoglobulin response and IgG3 response.

PilC, a 110 kD pilus associated protein was studied for function and localization. PilC is expressed from the pilC locus and N. meningitidis FAM20 expresses two PilC proteins, PilC 1 and PilC2 encoded by pilC1 and pilC2. PilC 1 and pilC2 are highly homologous but not identical. PilC1 and PilC2 share 84.7% similarity and 74.5% identity. PilC1 or PilC2 or both are essential for pilus biogenesis since pilC1-, pilC2- mutants were nonpiliated. In N. meningitidis, expression of PilC1, but not PilC2, contributes to attachment to host cells. Immunogold electron microscopy of cryosections and whole piliated bacteria indicated that PilC is located in the outer membrane and at the base of the pili.