Question

Question 1: How does the Mycobacterium initially evade the immune system? What role does the immune system play in preventing the spread of infection?

Question 2: Describe the difference between antigenic drift and antigenic shift? Which one is primarily responsible for the changes in the flu vaccine each year? Which phenomenon can lead to new pandemic strains?

Answer 1

1) Mycobacterium enters the body either by inhalation or by touching etc. First of all cell mediated immunity against the bacteria is not activated. So Mycobacterium will attach to the macrophages through Mannose and C3b receptor. Then it is engulfed inside the macrophage and phagosomal manipulation occurs . In this the maturation of the bacteria is halted and ineffective phagolysosome formation. This leads to unchecked bacillary proliferation and bacteremia with seeding of multiple sites.

After more than 3 weeks, cell mediated immunity develops and macrophage activates Tcell and transform it into Th1 cell. This T h1 secretes IFN-g which acts on macrophage. Macrophage gets activated and there is phagolysosome maturation and activation, production of nitric oxide, ros, autophagy, etc and the Mycobacterium is killed. Monocytes are recruited and Ultimately a granuloma is formed. This prevents the spread of infection. As the immune system tries to contain the bacteria inside the granuloma and limits the further spread.

2)

Antigenic drift	Antigenic shift
gradual, sequential change in the antigenic structure occuring regularly at frequent intervals.	abrupt, drastic and discontinuous variation in thr antigenic structure resulting in a novel virus strain.
New antigens are still related to the previous antigens so they react with antisera to the predecessor virus strains to varying degrees	antigenic structure resulting in a novel virus strain is unrelated antigenically to the predecessor strains.
It occurs due to mutation and selection	it occurs due to genetic reassortment
It accounts for the periodic epidemics of influenza every 2 to 3 years.	antibodies to predecessor viruses do not neutralize the new variants and therefore can spread widely in the population causing major epidemics or pandemics. It occurs every 10 to 20 years.
It most commonly occurs in type A Influenza and lesser in type B influenza.	It occurs in type A Influenza only.
It is responsible for changes in flu vaccine each year therefore it is mandatory to review the vaccine each year.