Which response type would typically take longer to develop upon first exposure to an antigen?

The primary response is the first immune response that occurs when the body is exposed to a new antigen. This response is characterized by a gradual buildup of antibodies and involves several steps. Initially, antigen-presenting cells (APCs) like dendritic cells capture and present the antigen to helper T cells. This leads to clonal selection and activation of B cells, which differentiate into plasma cells that eventually produce antibodies specific to the antigen.

The characteristics of a primary response include a longer lag phase, taking several days to weeks before antibodies can be detected in significant amounts. The immune system is essentially 'learning' how to recognize and fight this particular antigen for the first time.

In contrast, the other response types listed occur under different circumstances: the secondary response is rapid and robust because the immune system already has memory cells generated from the primary response. The adaptive response encompasses both primary and secondary responses but is not a term that specifically indicates the time frame; immediate response refers more commonly to innate immunity processes rather than adaptive immunity, which takes time to develop.

Hence, the primary response is correctly identified as the response type that takes longer to develop upon initial exposure to an antigen.