How does an Immune response is produced?

Different Components involved in Immunity


  • Cytokines – These are the small protein molecules involved in Signalling. Interleukins,  Interfereons, Lymphokines,chemokines comes under this class.
  • MHC (Major Histocompatibility Complex) – These are a set of surface proteins on almost all Nucleated cell surfaces and on APCs  to recognize the foreign substance.They display the peptide fragments of non-self proteins to the Leukocytes. Hence these are also called Human Leukocyte Antigen.
  • Cluster of Differentiation – These are transmembrane glycoproteins which serves as the CoReceptors of T-Cell receptors. They bind to the MHC molecules specifically,i.e.,  MHC-class I binds CD8 adhesion molecules onto Cytotoxic T cells, whereas  MHC-class II binds CD4 adhesion molecules onto T- Helper cells.
  • Complement system – It is a system of plasma proteins that complements(enhances) the ability of antibodies and phagocytes to destroy microbes, damaged cells and promotes inflammation.
  • Antibody – Also known as Immunoglobulin produced by plasma cells of B-Lymphocytes involved in neutralization of foreign particles like pathogens by Antigen-Antibody Interactions.
  • Antigen – Also known as Immunogen, a molecule capable of stimulating the immune cells to induce Immune response in host cell. In auto-Immune diseases, Antigen is a part of host itself.
  • Haptens – Small molecules which can induce immune response only when conjugated with a large carrier protein molecule. Antibodies raised against these molecules.
  • Epitope – The region on Antigen to which Antibody binds, an Antigenic determinanat recognised by the immune cells like T and B-cells.
  • Paratope – The region of Antibody to which Antigen binds, that is the part of antibody that binds to the epitope.
  • Phagocytosis – The process of engulfing foreign particle by the phagocytes is known as Phagocytosis. This is called Cell Eating.
  • Opsonization – It is aprocess of marking the pathogens for destruction during an Immune response. Opsonins are the molecules which Enhances the Phagocytosis.



How does an Immune reponse produced

  • Whenever an Antigen enters the host cell, it will bind to the host cell. The infected cell sends signals to the immune cells. 
  • Inflammation is a kind of Immune response. In this, Neutrophils, leaves the blood stream and moves towards the infected tissues by a process called Diapedesis. 
  • The detected antigens will be taken up by Antigen presenting cells, which presents the Antigens to the T-Cytotoxic lymphocytes. 
  • The APCs contains MHC(Major Histocompatibility Complex) I and II which activates Tcytotoxic and T-Helper cells.
  • Macrophages, dendritic cells present the antigens to the lymphocytes. If the antigen gets killed by Tc cells by cell mediated immunity.


  • Movement of Antigen towards the Phagocytic cell by  the process of Chemotaxis. The antigen attaches to the phagocyte.
  • By Endocytosis, the antigen slowly gets ingested into the phagocytic cell.
  • The antigen now can be called as a Phagosome as it is wrapped around by the host cell membrane.
  • This phagosome get fused with the lysosome of phagocytic cell and forms Phagolysosome.
  • As the lysosomes contain digestive enzyme secretions, the antigen in phagosome will be digested by the lysosomal secretions.
  • The residual body with indigested particles will be discharged as the waste material by a process of Exocytosis.

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