The proceeding of immunoglobulin class and subclass switching in 25 patients of common variable immunodeficiency was observed in vivo by using of vaccination with new-antigen bacteria-phage 174 (φx 174). 24 normal adults served as control. The pattern of anti-?x174 specific antibody response was as follows: IgM was presented first with decreasing rapidly

and IgG was coming late maintaining its high level long. The sequence of IgG subclass productions was in order of IgG3 and IgG1

IgG2

IgG4. There were special profiles of antibody response to φx174 in CVI patients: (l)class swithing defects: only IgM production in 9

IgM + + IgG3+IgGi in 5

IgM+IgG3 +IgGi + IgG2 in 6

and swithing from IgM to IgG4 ia only 4 cases; (2)the value of antibody response was low. Such fingings further indicate that the hypo-gammaglobulinemia of CVI resulted from defects in different levels of Ig class and subclass swithing along the 5’-3’ order of CH genes