Figure 1

Diagram of the immunologic effects of hyper IgM syndrome. A) In a healthy individual, the CD154 (CD40L)-CD40 interaction is essential for antigen-presenting cell (APC) maturation and B-cell antigenic shift towards the production of IgG, IgA and IgE. APC maturation leads to increased antigen-presenting capacity and phagocytic activity, as well as interleukin (IL) production that further stimulates T helper-1 (Th1) cell differentiation. B) In X-linked hyper IgM syndrome, CD40L mutations decrease the capacity of T-cells to differentiate and interact with other immune system cells, increasing susceptibility to opportunistic infections.