Microbiology Practice Exam

Which form of immunoglobulin is typically found in secretions like saliva and tears?

1. IgG

2. IgA

3. IgM

4. IgD

The correct answer is: IgA

The form of immunoglobulin typically found in secretions like saliva and tears is IgA. This antibody plays a crucial role in mucosal immunity, acting as a first line of defense against pathogens that enter through mucosal surfaces, which include the oral and respiratory tracts. IgA is specifically secreted in a dimeric form, meaning two IgA molecules are bonded together, offering enhanced stability and functionality in mucosal secretions. It can neutralize pathogens by preventing their adherence to epithelial cells and neutralizing toxins. Other immunoglobulins, such as IgG, primarily circulate in the blood and are involved in systemic immune responses, while IgM is the first antibody produced in response to an infection and is more prominent in the bloodstream rather than secretions. IgD functions mainly as a receptor on B cells, playing a role in the initiation of immune responses rather than directly participating in mucosal protection. Thus, IgA's unique properties and location make it the primary immunoglobulin found in secretions like saliva and tears.