What is the main function of IgA antibodies?

The primary role of IgA antibodies is to protect mucosal surfaces, which are critical points of entry for pathogens. IgA is predominantly found in mucosal areas such as the gastrointestinal tract, respiratory tract, and urogenital tract, as well as in secretions like saliva, tears, and breast milk. This localization enables IgA to act as a first line of defense by preventing the adherence and invasion of pathogens, neutralizing viruses, and facilitating the removal of antigens, thereby maintaining the integrity of mucosal barriers.

In addition to its protective role in mucosal immunity, IgA also contributes to immune exclusion by forming complexes with pathogens, which can then be cleared by mucociliary transport or with the aid of other immune cells. This functional aspect makes IgA vital for safeguarding against infections that target mucosal tissues, highlighting its specificity and effectiveness in those areas.

The other roles described in the other options are achieved by different classes of antibodies or are secondary functions; for instance, passive immunity is mainly provided by IgG and occurs during breastfeeding as IgA is passed to the newborn, while the activation of complement pathways is primarily mediated by IgG and IgM.