Lactating mothers provide immunity to their babies. If you were given your mother's milk, you got your mother's immunity. Read about that here.
Many companies sell freeze-dried colostrum and claim that it aids the immune system.
That is true, but so misleading that you have to get the full story here. ONLY a small part of the colostrum is actually helpful to the immune system. THAT part is called the transfer factor. It is extracted by a special process from the colostrum. Since there is a patent which greatly limits anyone's ability perform this extraction, many companies without access to that patent have started claiming immune-system building values to the colostrum itself.