SLAMF1 and X-linked lymphoproliferative disease: The interactions of GC B cells and TFH cells also require adhesion molecules of the signaling lymphocytic activation molecule (SLAM) family that signal through the adaptor SLAM-associated protein (SAP), as indicated by defects in the GC response in the genetic immunodeficiency disease X-linked lymphoproliferative syndrome (XLP), caused by loss of function mutations in SAP36.