How does the Immune Response work

Understanding the basic response process for foreign pathogens


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This articles content is derived from a correlation of various scientific explanations, with the purpose of simplifying the understanding, for a patient and caregiver just beginning their knowledge and learning journey.


What is a Immune response

The basic components that come together, to defend our bodies from foreign and harmful invaders.
The Definition of an immune response;
The body’s immune response to the presence of a foreign antigen.



Patrolling and detecting foreign invaders.
The immune system patrols for foreign (non-self) Antigens and Pathogens.

  • Antigens are essentially fragmented evidence of a cells anatomy, protein signatures on its surface. An ID or Passport.
  • Pathogens foreign invader cells – infectious agents (germs) that come from outside the body such as Bacteria and Viruses. Pathogens insert themselves are their corrupt snippet of DNA code, into a new healthy ost cell, that quickly replicates itself.



The Immune systems first responders are the “Antigen Presenting Cells” – (APC)

There are 3 types of APC Cells.
Macrophages, Dendretic Cells (DC) and B Cells.

The APC cells primary function is to consume antigens and pathogens, and showcase them on their surface to recruit a Helper T Cell Response.

Once a Helper T Cell is activated by an APC cell, it releases a storm of chemical messengers to recruit and amplify a greater immune response.

Let’s focus on 2 types of the 3 APC’s.

Macrophage Cells
These are large white blood cells that locate and ‘eat’ particles, such as bacteria, viruses, fungi, and parasites. (Pathogens).

Dendritic cells
These are cells found in tissue nearer to the outside of our bodies, such as skin, throat, Lungs and GI Tract.


More Explantions

B Cells are one of 3 types of Antigen Presenting Cells (APC) –
B Cell, Dendritic, Cells & Macrophages

Antigen Presenting Cells consume foreign invaders.
APC consumes foriegn antigens and their pathogens, they digest and showcase a sample of theses antigens at their surface through a receptor called MHC 2.
MHC 2 transports this digested sample from within the APC cell, to the exterior surface, like a warning flag with a sample fragment (Antigen) attached that attracts help. Help can then engage with the antigen and recruit more help from the immune systems Helper T Cells and B Cells.

APC Cells are of 3 types

  1. Dendritic Cells (DC)
  2. B Cells
  3. Macrophages

This Video highlights Macrophages as the APC example.

  • All Neucleated Cells have MHC 1 on their surface,
  • All APC Cells have MHC 2 as well. The 3 types of APC cells are Macrophages, B Cells, T Cells.
  • MHC (1) are receptors on the surface of all neckeated cells.
  • MHC receptors provide a presentation of material within the cell to the outside of the cell -a flag or a passport ID
  • MHC = Major Histocompatibilty Complex
  • MHC 1 is critical, as it is the mechanism that identifies the foreign invader within the cell (like a virus), it converts a sample of this virus material to be displayed / flagged on the cells surface to alert T Cells to destroy it.
  • CD8+ T Cells once interaction occurs with the infected cell, the Cell goes through a confirmation process. It the releases perferins that punch holes into the cell surface and then release granzymes to enter via the holes and downgrade  the cells dna/destroy the cells nucleus.
  • MHC 1 only interests with CD8+ Cyctotoxic Killer T Cells
  • MHC 2 only interacts with CD4+ T Helper Cells

MHC 1 attracts immediate Killer T Celll response
MHC 2 recuits the immune system to amplify ie more macrophages, and B Cells to producing plasma  that create antibodies that locate the foreign antigens, and also produce memory B cells for use at a later date. ie remember this threat.
MHC2 – When a APC cell and a Helper T Cell bind correctly via its ligands and receptors, this then activates the Helper T Cell to release cytokines (Chemical messengers) such as interleukind and interferon gamma to recruit and amplify the immune response.

Note: APC cells have CD = Cluster Differenttions on their surface. In this example  – CD 80 & 86  =CD 40.
Note: Also refers to CD4+ Helper T Cells having CD 28 receptors and CD 40 ligands on its surface to corresponspd /communicate with the APC cell.
Note All these CD’s need to match and bind to create activation.
Note Interleukins, interferons are part of the cytokine family.

Also view 

human epidermal growth factor receptor 2
Source – NCI 
A protein involved in normal cell growth. Human epidermal growth factor receptor 2 may be made in larger than normal amounts by some types of cancer cells, including breast, ovarian, bladder, pancreatic, and stomach cancers. This may cause cancer cells to grow more quickly and spread to other parts of the body. Checking the amount of human epidermal growth factor receptor 2 on some types of cancer cells may help plan treatment. Also called c-erbB-2, HER2, HER2/neu, and human EGF receptor 2.