TEKS 10A: Describe the interactions that occur among systems that perform the functions of regulation, nutrient absorption, reproduction, and defense from injury or illness in animals. â¢ B cells discover antigens in body fluids. â¢ T cells are released by infected body cells or immune cells that have encountered antigens. â¢ Vaccination stimulates the immune system with an antigen. The immune system produces memory B cells and memory T cells that quicken and strengthen the bodyâs response to repeated infection.