There are actually several that can help with your cats immune system
1)Echinacea which is an herb, also known as the purple coneflower are used for both humans as well as cats. It is very effective with several immune problems as it works by inhibiting viral and bacterial breakdown in the cell walls of your cat’s body.
This herb is also believed to stop several types of tumors from developing. It comes in a capsule form and is used generally for 6-8 weeks only as it effect on the immune system slows after this time frame.
2)Next is Vitamins A, E, and C. Vitamin A helps you cat with both their overall skin health as well as their eyesight. It is critical for their growth and helps to repair their body tissues. It is especially helpful in protecting what is called their epithelial tissues from becoming too thin. In doing so, it helps to protect your cat’s mouth, nose, throat, as well as their lungs. If these tissues become thin, it makes them much more subject to infection.
3)Vitamin E works with Vitamin A and helps to break it down in your cat’s body. Vitamin E is also extremely important to the cardiovascular system in your cat as well as helping to heal any type of wound, bruise, or worse yet, any type of burn. It also is believed to slow the aging process in cats.
4)Vitamin C is a very powerful antioxidant and as such helps protect the immune system against both viral and bacterial infections. It is also very powerful in protecting against most allergies that can attack your cat, but perhaps its strongest attribute is what it does for your cat’s blood vessels as well as collagen. It helps the blood vessels stay both strong as well as lucid which helps to prevent most types of hemorrhages, and it helps to maintain the collagen levels in your cat.
Collagen is a protein that helps with the proper development of you cats skin, their ligaments, as well as their bones.
Hope this helps, as all are very critical. However, what I do with my pets and have my daughters do for their cats is take on daily dosage of a very good name brand—there are several—liquid multi-vitamin. Liquids are far superior to any other form. Echinacea we use in a liquid capsule supplement form—but again, check first before you use this one.