Question

The Complement system combats microbes using which of the following (select all that apply)?

a. Induction of Inflammation

b. Opsonization

c. Phagocytosis

d. Recruitment of T-cells

e. Proteolysis of bacterial toxins.

Answer 1

All the options are correct.

Basically, complement system helps to remove the microbes and damaged cells from organisms. This is done by immune system that plays a crucial role that increases the ability of antibodies (secreated by plasma cells) and phagocytes to do this job. Phagocytes basically are the cells that eat up the foreign cells with the help of their plasma membrane.

Our complement system have number of small proteins that are synthesized by liver. These are not always active but remain as inactive precursors. When they are activated, proteases (enzymes which cleave specific proteins at specific site) cleaves proteins that inturn release cytokines (released in response to inflammation in body) and activates further cleavage.

In response to infection, various plasma proteins in complement system react with each other and inturn opsonization takes place i.e they make the pathogens more susceptible for phagocytosis so that they can be easily eaten up. This initiate series of inflammatory responses that fight the infection. Prior to opsonization, lysis also takes place means foreign bacteria are break down. Plasma proteins basicallt interacts with the pathogen, makes them susceptible and then phagocytes eats them up by phagocytosis.

Complement component 3 b (C3b) binds to the microbe causing opsonization and this inturn is recognized by C3b receptor by phagocyte receptor and thus microbe gets killed by creating the pores in the bacterial membrane. These receptors are the microbial carbohydrate and Fc receptor. After internalized by phagosomes, they get fused with lysosomes where the microbes are destroyed by reactive oxygen and nitrogen species and lysosomal enzymes.

Recruitment of T cells also plays important role in protection against intracellular pathogens. These T lymphocytes expresses T cell receptor and tends to express CD4 and CD8+ cells. They secrete cytokines (like interferon gamma) that activate macrophages and cytotoxic proteins in response to inflammation, after they are activated by the peptide antigens that are displayed by cell surface MHC molecules. Activated macrophages further produces oxygen species and nitric oxide synthase that makes nitric oxide. They are also found to increase the lysosomal enzymes that destroy microbes. This increases the function of phagocytosis.

Basically, antibodies are secreated in plasma and they get bind to pathogens or any foreign substance present and bacterial toxins present, where they carry out neutralization by cleavage of this toxins and foreign substance like bacteria by proteolysis.

So, all the options are correct.