Answer :
Final answer:
The mammalian immune system responds to an initial pathogen exposure with an innate response involving phagocytes like macrophages, followed by an adaptive immune response that gradually becomes effective over time.
Explanation:
When a mammalian immune system first encounters a pathogen, several steps occur in sequence to mount an effective defense. Initially, the innate immune system responds through inflammation and the production of protective proteins like complement and interferon.
The first cells to become active in the immune response are typically phagocytes, such as macrophages, which can immediately recognize and engulf invading pathogens. This process may involve pathogen coating with molecules like complement proteins that allow phagocytosis (as noted in option C). The adaptive immune system then follows, developing a primary adaptive response. However, during the first few days, the innate immune response can only partially control pathogen growth, with adaptive immunity becoming more effective over time, leading to pathogen clearance and the establishment of immunological memory for future, quicker responses.
Therefore, the primary disease represents the initial severe symptoms noticed during the first infection due to the time it takes for the adaptive immune response to kick in fully. After the encounter with the pathogen, memory B and T cells are developed, which will lead to a more rapid and strong adaptive immune response upon re-exposure to the same pathogen, showcasing the immune system's programmable memory.