INTRODUCTION
The mucosae are the largest surface areas of the body directly exposed to the environment and, in consequence, throughout life these surfaces are constantly challenged by microbes. Indeed, most infectious diseases take place or are initiated on these surfaces. The approximately 400 m2 of the mucosae in the respiratory, gastrointestinal, and genito-urinary tract of humans are protected by a multitude of innate and adaptive immune mechanisms (Ogra et al., 1999). To successfully colonise, all microorganisms, whether they are pathogens or commensals, must be able to evade local defence mechanisms. The dominant adaptive immune factor in the mucosal surfaces is secretory IgA (S-IgA), which is actively transported to the surface by a receptor-mediated mechanism. This chapter reviews the bacterial strategies to evade the functions of immunoglobulins (Ig), that involve proteolytic/glycolytic degradation or Ig-binding proteins, with a particular focus on IgA
IgA PROTEASE-PRODUCING BACTERIA
IgA proteases constitute a diverse group of bacterial proteinases that share several unique enzymatic properties including the ability to cleave human IgA in the hinge region. They are post-proline endopeptidases and, in most cases, attack the target polypeptide immediately adjacent to a carbohydrate side chain. With a single exception, the IgA proteases cleave only IgA1. The first examples of IgA1 proteases were demonstrated in Streptococcus sanguis, Neisseria meningitidis, and Neisseria gonorrhoeae by Plaut and coworkers in the mid-1970s (Plaut et al., 1974; Plaut et al., 1975).