Question

There are basically three different types of pathogen invasion “strategies” – extracellular, intracellular in non-phagocytes like epithelial cells, and intracellular in circulating phagocytes like Macrophages. That is, some bacteria try to remain outside of the host cells, while other bacteria and viruses get inside different types of host cells and survive there.

A. For EXTRACELLULAR pathogens, describe advantages and disadvantages of this strategy. How does our immune system detect and eliminate such pathogens? Explain two virulence factors that this sort of pathogen can use to survive in its chosen environment.

B. For pathogens that are INTRACELLULAR IN MACROPHAGES, explain how they gain access to macrophages. Describe advantages and disadvantages of this strategy. How does our immune system detect and eliminate such pathogens? Explain two virulence factors that this sort of pathogen can use to survive in its chosen environment.

C. For pathogens that are INTRACELLULAR IN EPITHELIAL CELLS, explain how they enter the epithelial cells. Describe advantages and disadvantages of this strategy. How does our immune system detect and eliminate such pathogens? Explain two virulence factors that this sort of pathogen can use to survive in its chosen environment.

Answer 1

Ans. A). Advantages:

-They have a greater chances to grow, reproduce, and spread rapidly.

-They can move to new cells or organs, when nutrients are less.

-They do not require host-to-host transmission.

Disadvantages:

-They have to face with complement proteins and antibodies.

-They have to compete with other pathogens and normal body flora.

Immune system recognizes the extracellular pathogens by T cells, with the help of MHC II (major histocompatibility complex II). T cells recognize digested peptide fragments of those pathogens.

Two virulence factors for this strategy are flagella and capsule.

B). Intracellular paathoens may gain access to macrophages by either having a rigid cell wall or by releasin proteins that resist damage by macrophages.

Advantages:

-They can remain hide from the immune defence responses of host.

-They can utilize resiources present inside the host cells.

Disadvantages:

-They have to exit the host cells to transmit another host.

Intracellular pathoens are killed by activated macrophages. The macrophages engulf and destroy many intracellular pathogens.

Two virulence factors for this stratey are glycolipid and pilli.

C). pathogens that live in epethilial cells enter through epithelium.

Advantages:

They have higher chances of colonization, localize inflammation, and spreading ue to epithelial cell turnover.

Disadvantages:

They have to deal with complement proteins and secretory antibodies, present in the muscosal secretion by epithelial cells.

These pathoens are killed by antimicrobila peptides and antibodies present in mucosal secretion.

Two virulence factors used by those pathoens are fimbriae and some bacterial toxins.