I finally got to ask a question this evening that has always irked me about immunology, regarding why weve even evolved to have T helper cells (specifically, Th2 cells) be required for B cells to pass a necessary developmental checkpoint in the adaptive (specifically, humoral) immune response. I think I proposed a really good answer, in that the presence of activated Th2 cells in at the edge of the lymph node follicle, which is what is required for activated B cells to begin secreting IgG, ensures that the subsequent negative selection checkpoint (antigen-presenting FDCs) is in place; if that developmental checkpoint werent there, then at times when FDCs were relatively absent, any activated B cells could differentiate to IgG-secreting plasma cells and could escape to the blood, regardless of the actual strength of their IgG affinity for antigen.
Posted on: Tue, 03 Dec 2013 06:54:03 +0000