Question

Both bacteria and phagocytic cells create toxins or harmful substances to

attack each other. In most cases, these substances could intoxify

themselves in the process. How do bacteria prevent toxic effectors from

targeting themselves and how do phagocytic cells prevent harmful

substances from damaging themselves?

Answer 1

Introduction: Phagocytosis is a process where microbes are engulfed by immune cells to destroy them. Several microbes such as bacteria and virus are destroyed by the process of phagocytosis. The immune cells such as neutrophils, lymphocytes and macrophages play an important role in the phagocytosis process. The phagocytosis process involves steps such as: pathogen recognition, formation of phagocytic vacuole, ingestion of phagosome, phagosome maturation to phagolysosome and destruction of the ingested pathogen inside the phagolysosome.

Explanation:

Bacteria that are pathogens produce toxins and produce biochemical substances that resist the defense against them. The bacteria have developed several strategies so as to avoid the engulfment and killing by phagocytes and aims at hindering the steps in phagocytosis. Bacteria produce several anti-phagocytic substances which are polysaccharide capsules, slime production and production of K antigens.

The strategies employed by some bacteria as defense against phagocytes include,

• Mycobacterium leprae have a waxy hydrophobic cell wall coat that contains mycolic acid and lysosomal enzymes. These bacteria grow inside phagocytic vacuoles that are not digested by lysosomal enzymes.
• Staphylococcus aureus is a Gram positive bacterium that produces enzymes catalase and superoxide dismutase. These substances neutralize the free radicals generated by the NADPH oxidase systems in phagocytes.
• The Gram-negative bacteria such as Salmonella typhi and Yersinia enterocolitica protect the peptidoglycan layer preventing the lytic activity of lysozyme.
• Listeria monocytogenes produce phospholipase C that lyse the phagosome membrane.
• Yersinia enterocolitica produces Yop proteins which are injected into the neutrophils killing the phagocytes.

Phagocytic cells in the immune system produce harmful substances that ingest and destroy pathogens such as viruses and bacteria and also other infected cells. These immune cells have mechanisms that produce chemicals to destroy the pathogens and neutralize the components produced by them.

Some chemicals produced are,

• Oxygen radicals which are produced during stress destroy cell structures of pathogenic bacteria.
• Antimicrobial proteins and enzymes such as protease, lysozyme and defensin are produced that attacks the cell wall and cell membrane of bacterial cells.

There are several cell surface receptors on the phagocytic cells or on the pathogens for easy recognition,

• Receptor cells called as scavenger receptors are produced by bacterial matrix which are proteins found extracellular. The pathogens easily identify this matrix as foreign substance and initiate the process.
• Toll like receptors are molecules that recognize specific bacterial pathogens and bind to them to activate an immune response.
• Antibodies are immune B lymphocytes that bind particular antigens present on the pathogenic cells by recognition of specific receptors.