Final answer:
Plasmacytoid dendrites are a major source of Type I interferons, especially interferon-alpha and interferon-beta. These compounds are crucial for the immune defense against viral infections. Within the adaptive immune system, T cells help B cells mature into plasma cells, which then produce antibodies.
Step-by-step explanation:
Plasmacytoid dendrites are specialized cells of the immune system that, when activated, are known to be a major source of Type I interferons, primarily interferon-alpha (IFN-α) and interferon-beta (IFN-β). These cytokines play a crucial role in the immune defense against viral infections. Given this context, the secreted compound of primary relevance from plasmacytoid dendritic cells is interferon.
In the broader context of the immune response, it is worthy to note that T cells contribute to the functioning of B cells. Cytokines secreted by T cells assist B cells in multiplying and maturing into antibody-producing plasma cells. Such plasma cells synthesize and secrete antibodies, including dimeric IgA in mucosal areas and pentameric IgM, which are vital for humoral immunity.
Plasma cells originate from B cells after their activation by antigens, upon which they undergo substantial changes. They stop expressing B cell receptors (BCRs) on their surface and focus resources on the production of antibodies specific to the antigens they encountered. Structurally, they are distinguished from B and T cells by an extensive endoplasmic reticulum required for robust antibody synthesis. Eventually, after performing their secretory functions, plasma cells are terminally differentiated, meaning they die off as their energies are not dedicated to self-maintenance, but to antibody production.