Antigen may be defined as the substance that are capable of generating an immune response. Antibodies are the substance that are generated to kill the antigen.
Immune complex is also known as antigen antibody complex. The immune complex is made up of the antigen and its specific antibody generated to kill that antigen.
The horse will give 32 chromosomes and donkey will give 31 chromosomes to the offspring. The offspring has 63 in total. It is odd so it can not produce normal germ cell. So it is sterile.