Question

1) Explain in your own words how immune system evasion represents a trade-off for the pathogen.

2) Describe an evolutionary explanation for why the human adaptive immune system has evolved to "react" to the presence of pathogens, rather than always be prepared to recognize and fight off any possible pathogen.

Answer 1

Answer 1: The five major types of strategy used by the pathogen for evasion  of host immune system are:

1: Antigenic distinguises

2. Immune supressor

3. Specific immune response

4. Induction of ineffective antibody

5. Antigenic variation

1: Antigenic distinguises: It is the process for antigen to hide inside some self molecule so antigen can only be detected by our immune system if it is free. As the pathogen is hiding themself inside our self molecule or cell so it is difficult for our immune cell to identify this as foreign molecule.Once inside the cell they grow and divide to show their action.

2.Immune suppressor: The pathogen act here very smartly. When the attack of pathogen occur so they do not start dividing simultaneously.Once inside the body some pathogens go to hind in some place for long time and they wait for our immune system to think as everything is fine as a result of this our immune system is suppressed now after this suppression the pathogen start to divide.

For example the pathogen responsible for typhoid once inside the body it firstly go to stay in our gall bladder for 7-8 hours. so when all the immune cells are becoming inactive then after this time period it start to divide.

3.Specific Immune Response: As our whole tissue or cell  do not contain the specific immune cell in proper proportion means there are some regions in our body which do not contain any immune receptors, so the pathogens like to hide in those regions so it will escape from immune response.

As we know that we have COP cells in our immune system which is called as macrophage killing cells. The pathogens are hiding in the place where COP can not go.

4.Induction of ineffective antibody: It is also a smart way of pathogen to fool our immune cells. Here bacterial cell or pathogen is going to secrete some molecule which is immunogenic but it is not harmful to the host with some little amount of antigens. Means the pathogen here itself act as antigen and it also secrete some molecule which is immunogenic but less toxic to host.

As the antigen secretion(which is dangerous) is producing in less amount as compaired to other compound which is produced in large amount( immunogenic but less toxic) so our immune system start to act firstly on large number of cell which is immunogenic and in course of this the pathogen will be escaped from immune system.

5. Antigenic variation: The antigen can change the arrangement of some gene so they can attack the host cell again and again.

If the host cell is encountered with the some type of infection so there is chance of development of memory cell for second encounter of the same pathogen. So in this case for second time infection the gene is going to have different combination of a particular protein. As  we know that a specific protein is generally responsible for addition to host cell as PilE protein have 6 different combination of gene for its attack.