The Beautiful Immune System Lesson 4: Humoral and Cell-Mediated Immunity

If you haven’t been following my “beautiful immune system” lessons, I highly suggest you go back and read the first three lessons to catch up. These are short and simple lessons leading you through what will eventually be a great understanding of how the immune system works. I hope you enjoy! To the Beautiful Immune System Lessons.

Adaptive immunity (and innate immunity) can be separated further into two types of immunity: humoral immunity and cell-mediated immunity.

Humoral, coming from the word humors, or “body fluids”, is the immunity that takes place in the extracellular (not within cells) fluids of the body such as the blood and lymph.

Innate Humoral Immunity Players:

• The Complement System is a biochemical cascade (a complicated pathway, with one reaction leading to another and so on) made up of blood plasma proteins. Once an intruder has been identified by the body, these proteins work together to kill or mark the intruder for destruction. This is mainly classified as part of the innate immune system, however it does also involve parts of the adaptive immune system.

Adaptive Humoral Immunity Players:

• B Cells are lymphocytes that make antibodies to microbial antigens.
• Antibodies are released by B cells and can be found circulating in the blood, bodily secretions, and tissue fluid, in response to a foreign antigen introduced to the body. Once an antibody binds to its specific antigen, it stimulates the immune system to respond appropriately.

Cell-mediated immunity is just how it sounds; specific cells are put to work when responding to foreign invaders.

Adaptive Cell-Mediated Immunity Players:

• Macrophages engulf and digest foreign invaders. Then they use the fragments of the antigens and display them on their cellular surface.
• Helper T cells bind to the antigen fragments on the surfaces of macrophages and secrete chemicals that signal other cells to start fighting, especially cytotoxic T cells.
• Cytotoxic T Cells, or “killer T cells”, begin to make clones of themselves once activated. These cells are specific to the invader whose antigens triggered the cascade of responses. Killer cells bind to infected cells and release chemicals that are lethal to the microbe-infected cell.
• Cytokines are small proteins that are involved in cell signaling and provide a balance between humoral and cell-mediated responses.

Check back for more detailed posts about each of these “players”.

Resources:

1. Abbas, Abul K., Andrew H. Lichtman, and Shiv Pillai. Cellular and Molecular Immunology. Philadelphia: Saunders Elsevier, Inc., 2010.