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# Microbiology Definitions This document defines key terms related to microbiology, immunology and related topics. ## Microbe * **Definition:** Microscopic organisms residing in water, soil, air. * **Types:** Bacteria, fungi, algae, protozoa, viruses, parasites. * **Further notes:** Some ar...

# Microbiology Definitions This document defines key terms related to microbiology, immunology and related topics. ## Microbe * **Definition:** Microscopic organisms residing in water, soil, air. * **Types:** Bacteria, fungi, algae, protozoa, viruses, parasites. * **Further notes:** Some are pathogenic, while others are beneficial to human health (commensal). ## Antigen * **Definition:** Any substance triggering an immune response in the body. * **Mechanism:** Reacts specifically with resultant antibodies or generated immune cells. ## Cytokine * **Definition:** A type of protein affecting the immune system. * **Function:** Can either boost or suppress the system. * **Production:** Naturally occurring or laboratory-produced. ## Antibody (Immunoglobulin - Ig) * **Definition:** Special proteins created by white blood cells, specifically activated B cells. * **Function:** Kill or weaken infection-causing organisms. Travel through blood looking for pathogens. * **Further notes:** Also crucial for the body's response to new pathogens or vaccines. ### Specific Immunoglobulins (Ig) | Immunoglobulin (Ig) | Characteristics | |---|---| | IgA (Immunoglobulin A) | Secretory form found in linings of the respiratory tract, digestive system, saliva, tears and breast milk (colostrum). Acts as an antiseptic paint on mucous membranes. Can activate the complement system in the presence of lysosomes to kill certain organisms. Serum IgA cannot activate the complement system.| | IgD (Immunoglobulin D) | Found in blood in low levels. Cannot activate the complement system. Approximately half of antigen-specific receptors on B lymphocytes are composed of IgD antibodies.| | IgE (Immunoglobulin E) | Found in serum in small amounts. Primarily attached to mast cells and basophils (granulocytes). High levels associated with allergies (e.g., asthma/hay fever).| | IgG (Immunoglobulin G) | Most common antibody in blood/tissue fluid. |