Question

Please discuss/define what type II hypersensitivity is. What antibodies are involved? What is the immune system trying to recognize if the antigen is considered self or non-self? Discuss an example where this would come into effect.

Answer 1

Type II hypersensitivity is mediated by an antibody IgG. This antibody will be target cell surface antigen and destroyed the cell via complement activation or ADCC (explained below). Examples include autoimmune hemolytic anemia, erythroblastosis details, etc. Details of type II hypersensitivity has been discussed below.

Type II antibody involves the antibody-mediated killing of cells. The antibody binds with the receptors on the target cells and activate the complement system and kills the cell by creating pores in the membrane of the target cell )(Figure). The second mechanism of target cell destruction is antibody-dependent cell-mediated cytotoxicity (ADCC). In this, Fc receptors present on the cytotoxic cell interact with the Fc region of the antibody bound to the receptors on the target cell and promote the killing of the target cell (Figure).

e.g. is Erythroblastosis fetalis.

In the first pregnancy, Rh-negative mother containing fetus with RBC + Rh antigen gets exposed to the Rh antigen during fetus birth. Exposure of Rh antigen to the mother will generate IgG antibodies with the memory cells for the Rh antigen. During the second pregnancy of the fetus containing Rh antigen; the presence of IgG antibody for Rh antigen in the mother will cross the placenta and react with the RBC containing Rh antigen of the fetus and causes erythroblastosis fetalis.