The dual function of the splenic marginal zone: essential for initiation of anti‐TI‐2 responses but also vital in the general first‐line defense against blood‐borne antigens
The splenic marginal zone (S‐MZ) is especially well equipped for rapid humoral responses and is unique in its ability to initiate an immune response to encapsulated bacteria (T‐cell independent type 2 (TI‐2) antigens). Because of the rapid spreading through the blood, infections with blood‐borne bacteria form a major health risk. To cope with blood‐borne antigens, a system is needed that can respond rapidly to a great diversity of organisms. Because of a number of unique features, S‐MZ B cells can respond rapid and efficient to all sorts of blood‐borne antigens. These unique features include a low blood flow microenvironment, low threshold for activation, high expression of complement receptor 2 (CR2, CD21) and multireactivity.