explain why it might take several weeks after exposure to HIV for a peron's HIV antibody test to be positive

Answer 1

In order for an antibody test to be positive, the body must be producing a measurable amount of antibodies. It takes some time (weeks) for a person's body to produce enough anitbodies to HIV to be measured.

Answer 2

It takes a while for the virus to enter the body, replicate and infect its target cells (T cells and macrophages, among others). It also relates to the way the immune response matures. When you are first exposed to a new pathogen, e.g. HIV, the antibodies you make are of the subtype IgM (Immunoglobin type M). The B cells making these antibodies become activated by T helper cells, and go through a complicated process of cell division called clonal expansion, during which two things happen. 1. some of the cells undergo mutation in their antigen-binding portion of the antibody genes, which may generate higher-affinity antibodies which bind better to the HIV antigens. 2. class switching from IgM to IgG. This process takes a couple of weeks

The antibody test for HIV looks for the IgG antibodies.

Answer 3

Check here.
http://en.wikipedia.org/wiki/HIV_test

The key thing it's testing for antibodies, not HIV itself.