Final answer:
Vaccines aimed at enhancing IgA antibody production, such as the influenza vaccine, target mucosal immunity to protect against pathogens entering through mucous membranes. Selective IgA deficiency leads to increased susceptibility to infections in the respiratory and gastrointestinal tracts due to the pivotal role of IgA in neutralizing pathogens at these entry points.
Step-by-step explanation:
Vaccines that induce a predominantly IgA response are those that are formulated to enhance the production of IgA antibodies, which are critical for the defense against infections that commonly enter the body through mucous membranes. An example of such a vaccine is for influenza, which utilizes mucosal delivery to trigger IgA production in the mucous and other secretions of the body. The mucosal immune response is essential because IgA (and sometimes IgM) antibodies in these secretions can bind to pathogens and neutralize them, preventing them from binding to receptors on cells and establishing infections.
Individuals with selective IgA deficiency are more susceptible to respiratory and gastrointestinal infections due to the lack of secretory IgA, which serves as a first line of defense in these areas. Without adequate IgA, individuals may have reduced capacity to neutralize pathogens and are therefore at greater risk for infections by a variety of bacteria and viruses such as H. influenzae, S. pneumoniae, and Giardia lamblia.