A person who has a weakened immune system may not be able to fight against infection because pathogens may enter the body and cause illness.
phagocytes may enter the body and cause illness.
normal cells crowd out unhealthy cells.
antibodies production is increased.

which

the cover letter for a job search includes the skills one has for the particular job. including a cover letter is always a good idea, as it describes the ability to perform a task, and the employer can easily fetch the intention of the job you want to do.  

the cover letter is very important to be included in the job search document. hence, i strongly with the statement.