MadSci Network: Immunology

Re: What is the natural immune response to the polio virus?

Date: Thu Mar 15 15:17:55 2001
Posted By: Art Anderson, Senior Scientist in Immunology and Pathology at USAMRIID
Area of science: Immunology
ID: 984385524.Im

Dear Bubbles,

There are a lot of key words in your sentence that have "specific" meanings in immunology so your use of them might complicate my answer. Let me start with a glossary.

There is something called NATURAL IMMUNITY which includes Natural Antibodies and Natural Killer cells. This kind of immunity exists without having to introduce an antigen or pathogen stimulus. The responses are directed against common antigens that are found in a lot of organisms and may even be found normally in the animal making the Natural Immunity. Phosphoryl Choline is one of these antigens. It is found in bacterial cell walls but it is also found in red blood cell membranes and other cell membranes when they break down. Immunity to it may be part of the bodies way of cleaning up rubbish left over from the wear and tear of life. The antibodies also my slow down a pathogen briefly when it invades the body.

Acquired Immunity is the kind of immunity you are asking about, I think. This kind of immunity is always "specific", meaning it is directed only at the particular virus or antigen that stimulated it and another different virus introduced in such an immune individual will not be resisted.

The second part of your question involves a different kind of specificity. I go to great length to explain this in my web site on Critical Issues in Vaccine design. In brief, viruses (bacteria and parasites as well) have ways of using some of the hosts own biology to find an advantage after invading the body. These "tricks" involve use of molecules that mimic normal molecules found in the animal this organism infects. The effect of these molecules is to create "specificity" in the way the body responds to each virus or other pathogen so that the kind of immunity may be very different for one virus than it is for the other. Route of viral invasion, kind of mimicked host protein, and ability to trigger the host to up-regulate (induce to appear, increase amount or secrete) specific hormones, proteins etc are ways a disease producing virus can alter how our body responds to it. In some cases the virus induces the body to respond with mostly an antibody response. This does the virus a favor because it may be relatively resistant to antibody and killer T-cells are needed to eradicate it. Catch-22, when antibody is emphasized killer T- cells could be the virus an advantage and vice versa. In designing vaccines these tricks and the molecules used by the virus to carry out the tricks need to be known so that the proper kind of immunity develops.

Among tricks a virus uses to gain advantage include using some of the molecules required by the host immune system for its function as targets for its infection of the host. This is what the Human Immunodeficiency Virus [HIV] does when it uses the CD-4 molecule and a chemokine receptor to invade T-cells. The CD-4 molecule is on helper T-cells that are important in regulating the initiation of immune responses. The CD-4 molecule is important in cell interactions needed for the function of these cells. Chemokine receptors on T-cells have recently been found to be a second molecule that the HIV virus uses to get into the cell. Chemokines are important small molecules that control adhesion, migration and traffic of lymphocytes from blood into lymphatic tissues and places where immune responses take place.

So, Bubbles it seems that each virus is different and despite the specificity of an immune response the virus itself has specific ways to disrupt that specificity so that the kind of immunity to viruses is always going to be different from that of another. Maybe this is why, after all these years of making vaccine candidates by thousands of scientists we only have a handful of safe and effective vaccines and luck was an important part of those successes. In many serious situations luck is that missing ingredient. We have to continue to toil at science in order to be there with the right tool at the right time so luck has a chance.

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