sentences:  In this case, Ca alloantibodies are thought to actually suppress a response against Aa blood groups, and therefore these mares do not make Aa alloantibodies if the foal has both Ca positive and Aa positive blood.These natural alloantibodies have not been shown to produce isoerythrolysis in foals, and are actually thought to help prevent NI by desensitization of the immune system and preventing the more harmful Aa alloantibodies from forming.Alloantibodies against De, Ua, Pa, and Ab blood groups have also been associated with neonatal isoerythrolysis.