Answer
Phagocytosis will not be successful, if the phagocyte cannot bind to the pathogen. In order for the phagocyte to adhere to the pathogenic organism, the phagocyte must recognize the carbohydrate signature of the pathogen. However, some microorganisms have an external capsule that prevents the phagocyte from identifying their carbohydrate signal and binding with them. This defeats phagocytosis. This resistance to phagocytosis can be overcome by opsonization of the pathogen . This provides a biochemical "handle" which enables the phagocyte to grasp and destroy the pathogen..
Some microorganisms like tuberculosis bacteria resit the action of lysozymes ; this also stymies phagocytosis. In this case, helper T cells come to the rescue; they can release certain chemicals that stimulate the phagocyte to produce deadly toxins--superoxides and other free radicals. Helper T cells can cause the generation of hydrogen peroxide, and activate other digestive by modifying the pH in the phagolysosome.
Work Step by Step
Neutrophils have an additional weapon against resistant pathogens. They release antimicrobial peptides called defensins into the extracellular fluid to destroy microorganisms.
