What must the immune system do first to provide protective immunity?

The immune system's initial step in providing protective immunity is to engage the microorganism. This engagement typically involves the recognition of the pathogen by immune cells, such as dendritic cells and macrophages, which play a critical role in identifying foreign invaders. This process is essential because it sets the stage for a coordinated immune response.

Once the pathogen is recognized, immune cells can present antigens from the microorganism to T cells, which then become activated and proliferate. This activation is crucial for the subsequent responses that lead to pathogen elimination. Engagement is necessary to determine the specific type of immune response needed, whether that involves the production of antibodies by B cells or the cell-mediated response by T cells.

Without this initial engagement, the immune system would lack the necessary information to mount an effective response, highlighting the importance of this first step in establishing protective immunity.