CD4 and endothelial dysfunction: However, damage to the endothelium, and subsequent endothelial dysfunction and activation, is followed by acute phase responses and alteration in coagulation and in the cytokine network, together with transient immune dysregulation, characterized by reduction in circulating peripheral CD4+ T lymphocytes and perivascular infiltration by CD4 and CD8 T lymphocytes, B cells, and macrophages, all features collectively termed as “rickettsial vasculitis”.