HP and immune system disorder: Hp infection can cause strong humoral immune response.19 Children with peptic ulcer may develop humoral immune disorder characterized by increased lymphocyte levels.13 In our study, the level of IgG in children with peptic ulcer was higher than that in healthy children, yet without significant difference in IgA, IgG and IgM levels between children with Hp-positive ulcer and those with Hp-negative ulcer.