Final answer:
Specific antibodies are detectable in serum following primary contact with antigen after 5-7 days due to the primary antibody response. The lag period allows for essential steps in the immune response to occur, leading to the production of specific antibodies.
Step-by-step explanation:
Specific antibodies are readily detectable in serum following primary contact with antigen after 5-7 days because of the immune response known as the primary antibody response. The lag period of approximately 10 days is required for all the steps of the primary response to take place, including antigen processing and presentation, helper T cell activation, B cell activation, and clonal proliferation.
During this lag period, no antibodies can be detected in the serum. However, after the lag period, the levels of IgM antibodies in the serum rise, followed by IgG antibodies, resulting in the detection of specific antibodies.