עברית: T Independent B Cell Activation. TI-1 induce plasma cell differentiation through dual activation of B cell receptors and innate PRR receptors. TI-2 antigens are not mitogenic, but induce antibody synthesis and secretion. These antigens are characterized by highly repetitive pattern, thus allowing cross-linking of many B cell receptors. Also, many of these antigens are opsonized by the complement system before reaching the designated B cell. This property is being exploited by the B cell coreceptor complex, comprising of the complement receptor 2 (also known as CD 21), and two additional proteins CD19 and CD 81.