| A | B |
|---|
| Area where B cells become immunocompetent. | bone marrow |
| Area where T cells become immunocompetent. | thymus |
| Area where activated immunocompetent B and t cells recirculate. | blood and lymph |
| Area seeded by immunocompetent B and T cells. | lymph nodes, spleen and other lymph tissues |
| Area where antigen challenge and clonal selection are most likely to occur. | lymph nodes, spleen and other lymph tissues |
