Immune System Composition

Immune System Composition

• The immune system consists of two main parts: innate immunity and acquired immunity.

Innate Immunity

• Does not depend on previous exposure to antigens
• Not specific
• Creates no memory
• Cannot alter the size of its response to an antigen

Acquired Immunity

• Specific
• Capable of recognizing non-self in a highly specific manner
• Creates a memory of the antigens it encounters
• Developed by exposure to antigens (pathogens)
• Involves lymphocytes and the antibodies they create
• Ability to amplify an immune response when under heavy attack from antigens
• Lymphocytes are created within bone marrow and mature within either bone marrow or thymus

Lymphocytes

• Two main types: T-Lymphocytes (involved in cellular reactions) and B-Lymphocytes (produce antibodies)

B-Lymphocytes

• Stimulated to multiply into blast cells that become either memory cells or antibody-secreting lymphocytes upon contact with a pathogen (antigen)

Antibodies

• Large soluble protein molecules produced by B lymphocytes
• Specifically designed to “fit” onto specific antigens and neutralize them or facilitate their destruction
• Made up of immunoglobulins (glycoproteins found in serum and tissue fluid of mammals)
• Five classes: IgG, IgM, IgA, IgD, and IgE

Immunoglobulin Classes

• IgG: most abundant (70-75% of serum immunoglobulins), contributes to long-term immunity
• IgM: largest antibody, created during primary response (first exposure to a new antigen)
• IgA: found in mucosal linings (intestines), tears, saliva, colostrum, respiratory system, and genitourinary tract
• IgD: function not specified in this context
• IgE: function not specified in this context

Antibody Function

• Latch onto the antigen, forming an antigen-antibody complex that captures the antibody and neutralizes it
• Allow other immune cells to come in and destroy the antigen
• Can signal to other cells to encourage phagocytosis and initiate complement on the antigen

Active Acquired Immunity

• Created by exposure to a pathogen (antigen), either naturally or artificially through vaccination
• Natural active acquired immunity: created by a pathogen infecting an individual, takes time to create antibodies, and signs of disease may be seen
• Artificial active acquired immunity: created by vaccination, involves deliberate exposure to antigen without causing disease