2.7 Overcoming Host Immunity

Pathogens have many strategies, depending on their type, against the hosts defense system. Obligate intracellular bacteria, for example, need the host cells to replicate. They employ many adaptive strategies to overcome our body’s antibacterial immune response to cause infection successfully.

One such method is the coat change strategy. The cell wall is the first line of defense a bacterium has against the immune system, and it is also the first indicator for our immune system when it comes to recognizing the pathogen.

For example, E. coli is a gram-negative bacterium that acylates the lipid A in its cell wall, making it gram-positive. This masking allows it to repel the positively charged immune cells of the hosts defense system. Similarly, other pathogens try and mask their structures from the immune system to not get detected or bypass the first response to spread in the body.

Another strategy that viruses commonly use against the host defense system is antigen drift. This occurs through specific genetic mutations in the virus’s surface proteins, for example, influenza, namely in HA (hemagglutinin) and NA (neuraminidase). These antigens are markers that our immune system recognizes and knows to target when encountered.

Over time, changes in the surface proteins produce similar but slightly different viruses that eventually cannot be recognized by our immune system due to the mutated antigen markers.

Once antigen drift has occurred, our immunological memory no longer serves us against the virus.

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