BAFF (B cell activating factor), also referred to TNFSF13B (Tumor necrosis factor superfamily, member 13B) or CD257 antigen, is a type II membrane protein with 285 amino acids, located at the human chromosome 13q33.3. It is a fundamental survival factor of 31.2 kDa for B cells and belongs to the tumor necrosis factor (TNF) family. This cytokine is expressed on T cells, dendritic cells, macrophages, and monocytes, but not by B cells. BAFF is a ligand and is required for peripheral B-cell mature, survival and homeostasis. It is also involved in the regulation of expression on certain B-cell-surface proteins, such as CD21 and CD35. BAFF deficiency reduces the amount of B cells and result in a diminished ability to build robust humoral immune responses. B7RP1 (B7­related protein) is also referred to B7­H2 (B7 homolog 2), CD275, and ICOSL (ICOS Ligand) in human. B7RP1 is a single-pass type I transmembrane glycoprotein, which belongs to the B7 family of the immunoglobulin (Ig) superfamily. B7RP1 is primarily expressed on antigen presenting cells including B cells, macrophages, monocytes, and dendritic cells. B7RP1 is the ligand for ICOS (CD278), a member of the CD28/CTLA4 family of co-stimulatory receptors. The B7RP1/ICOS interaction plays roles in T cell dependent B cell activation and Th (T helper) cell differentiation, leading to both positive and negative effects on immune responses. B7RP1 also binds to CD28 and CTLA4, and its interaction with CD28 can co-stimulate T cells. B7RP1 is associated with the development of allergic asthma and other autoimmune disease.