Tag: active and passive immunity

During infection, B-cell receptor binds to the antigens and these bound antigens are engulfed into the B-cells by receptor-mediated endocytosis. The antigens are then degraded, and presented to T cells in complex with MHC-II (major histocompatibility complex - II) molecules on the cell membrane. T-cells bind to the B-cells and secretes lymphokines due to which B-cell undergo proliferation and produce antibodies specific to the antigen.

An antigen is a foreign substance which produces an immune response and is specifically bound to antibodies. Each antibody is specifically produced by the immune system to match an antigen after cells in the immune system come into contact with it, this allows a precise identification or matching of the antigen. Antigens are usually proteins, peptides and polysaccharides which elicit an immune response.

A cytotoxic T-cell, also known as Killer T-cells is a T lymphocyte (a type of white blood cell) that kills cancer cells, cells that are infected (particularly with viruses), or cells that are damaged in other ways. When killer T-cells are exposed to antigens, they release the cytotoxins perforin, granzymes, and granulysin. Perforins and granzymes causes pore formation in the antigen which causes the intracellular content of antigen to leak out resulting in cell death.

Memory cells are formed from T-lymphocytes because memory T cells have the ability to recognized specific antigen. They will activate a stronger and faster immune response after they come across the same antigen again

The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, T cells mature. T cells are critical to the adaptive immune system, where the body adapts specifically to foreign invaders. The thymus is the largest and most active during the neonatal and pre-adolescent periods.  Surgical removal of the thymus results in immunodeficiency because T- cells do not undergo maturation and this results in suppression of the immune system. 

They have a long life which might start from few months and range to their entire life.

Humoral immunity is a type of immunity which is mediated by macromolecules found in extracellular fluids such as secreted antibodies, complement proteins, and certain antimicrobial peptides. Humoral immunity is so named because it involves substances found in the humour or body fluids. It involves B-lymphocytes or plasma cells and is often known as antibody-mediated immunity.

• T-cells are a type of white blood cell that plays a central role in cell-mediated immunity. 
• T-helper cell assists other white blood cells in immunologic processes, including maturation of B cells into plasma cells and memory B cells and activation of cytotoxic T cells and macrophages. These cells are also known as CD4+ T cells because they express the CD4 glycoprotein on their surfaces.
• Cytotoxic T-cells destroy virus-infected cells and tumour cells and are also implicated in transplant rejection. These cells are also known as CD8+ T cells since they express the CD8 glycoprotein at their surfaces.
• So, the correct answer is 'CD 4'.

• The immune system is a host defence system comprising many biological structures and processes within an organism that protects against disease.  The immune system can be classified into subsystems such as the innate immune system and the adaptive immune system, or humoral immunity and cell-mediated immunity. 
  
• Humoral immunity is the aspect of immunity that is mediated by macromolecules found in extracellular fluids such as secreted antibodies, complement proteins, and certain antimicrobial peptides.
  
• Cell-mediated immunity is an immune response that does not involve antibodies, but rather involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.
  

So, the correct answer is 'Humoral and cell-mediated systems'.