In immune response, how is the secondary response to an antigen different from the primary response?
The primary immune response to an antigen concerns the identification of the antigen and the development of the proper immune response; while the antigen is being identified, T-cells which kill indiscriminately are deployed. Primary response can take up to two weeks, resulting in the conversion of some T-cells to B-cells (memory cells). The secondary response to an antigen concerns the activation of B-cells which have been trained by the primary response to react to that specific antigen; the secondary response is faster, more efficient, and leads to a stronger defense than the primary response. One good example of primary/secondary response is vaccination. Vaccines consist mainly of dead or weak disease cells or viruses, which are introduced into the body. The immune system reacts to this weak hostility with a primary response, creating B-cells which remember how to kill the vaccine. When the full-powered disease or virus attacks, the immune system begins a secondary response, using its prior knowledge of the vaccine to swiftly and powerfully attack and kill the invading disease.
Primary immune response is when your body is first exposed to an antigen, the first time it comes in contact with that foreign material. An antigen is anything that is recognized as non-self, so it ranges from pollen to bacteria or viruses.
The primary immune response takes 5-10 days to effect the antigen, since it has to find the correct antibodies to eliminate the antigen. This response is also called the innate or non-specific immune response.
Once your body has "found" the antibody, it will store some of the cells as B cells that stay in your lymph nodes. This is so when your are exposed to the antigen again, and it travels through your lymphatic system, it will reach an antibody that recognizes it, and your body doesn't need to make brand new antibodies--it just needs to start cloning the antibody that matches that antigen. This is the secondary response, and it generally only takes 3-5 days for a system-wide response, since you already have the antibody, it just needs to pick up the antigen before it starts dividing into new cells.
The T cells are generally used in the primary response to the antigen, since cytotoxic T cells kill whatever they touch, while the more specific B cells are used in the secondary response, since they are honed in to that antigen already, and will not kill off healthy, self-cells.