Immunology First Lecture PDF

 Other Chemical Barriers In addition to the previously mentioned chemical factors of physical barriers,blood, lymph, and other body fluids contain a collection of defensive chemicals such as bacteriocins, betalysin, and other polypeptides. 1. Bacteriocins - Ma...

 Other Chemical Barriers In addition to the previously mentioned chemical factors of physical barriers,blood, lymph, and other body fluids contain a collection of defensive chemicals such as bacteriocins, betalysin, and other polypeptides. 1. Bacteriocins - Many of the normal bacteria synthesize and release plasmid-encoded toxic proteins (e.g., colicin, staphylococcin) called bacteriocins that are lethal to related species. - Most bacteriocins are peptides or proteins and are produced by gram-negative bacteria. However, some gram- positive bacteria produce bacteriocin-like peptides. - For example, E. coli synthesizes bacteriocins called colicins, which are coded for by different plasmids. Some colicins: a. Bind to specific receptors on the cell envelope of sensitive target bacteria and cause cell lysis, b. Attack specific intracellular sites such as ribosomes. c. Disrupt energy production. 2. Beta-Lysin and Other Polypeptides a- Beta-lysin is a cationic polypeptide released from blood platelets. - It can kill some gram-positive bacteria by disrupting their plasma membranes. - Other cationic polypeptides include leukins, plakins, cecropins, and phagocytin. b- A zinc-containing polypeptide, known as the prostatic antibacterial factor, is an important antimicrobial substance secreted by the prostate gland in males.