Many probiotics claim to support immune health but it is important to understand that different strains affect the immune system in different ways. Lactobacillus strains stimulate the immune system causing an increase in white blood cell production, this is referred to as cellular immunity. Bifidobacteria support humoral immunity and help calm the immune response. For someone with an over-active immune response, a probiotic containing only Bifidobacteria would be the best option. Theralac contains both types of strains which is ideal for many people. TruFlora stimulates the immune system with Lactobacillus strains while TruBifido contains only Bifidobacteria for those that need to regulate the immune response and not stimulate it further.