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Immune System & Disease Cheat Sheet
A printable reference covering innate immunity, adaptive immunity, antibodies, vaccines, inflammation, pathogens, and disease transmission for grades 10-12.
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The immune system protects the body from pathogens such as viruses, bacteria, fungi, and parasites. This cheat sheet summarizes the major defenses used to recognize, attack, and remember disease-causing agents. Students need these ideas to understand infection, vaccination, allergies, autoimmune disease, and public health. It is designed as a quick reference for biology review, labs, and test preparation. The immune response begins with barriers and innate defenses, then may activate adaptive immunity. Innate immunity includes skin, mucus, inflammation, fever, phagocytes, and natural killer cells. Adaptive immunity depends on B cells, T cells, antibodies, antigens, and memory cells. Key disease concepts include transmission, incubation period, herd immunity, R0, and vaccine effectiveness.
Key Facts
- Innate immunity is fast and nonspecific, while adaptive immunity is slower at first but highly specific to particular antigens.
- An antigen is a molecule recognized by immune receptors, and an antibody binds a matching antigen using a specific lock-and-key fit.
- B cells can differentiate into plasma cells that secrete antibodies and memory B cells that respond faster after re-exposure.
- Helper T cells activate B cells, cytotoxic T cells, and macrophages by releasing signaling proteins called cytokines.
- Cytotoxic T cells kill infected body cells by recognizing antigen fragments displayed on MHC I proteins.
- Phagocytes such as macrophages and neutrophils engulf pathogens using phagocytosis: pathogen + phagocyte -> phagosome -> digestion.
- Basic reproduction number R0 means the average number of new infections caused by one infected person in a fully susceptible population.
- Herd immunity threshold can be estimated by H = 1 - 1/R0, where H is the fraction of the population that must be immune.
Vocabulary
- Pathogen
- A disease-causing agent such as a virus, bacterium, fungus, protist, or parasite.
- Antigen
- A molecule or molecular pattern that the immune system recognizes as foreign or abnormal.
- Antibody
- A Y-shaped protein made by plasma cells that binds a specific antigen and helps neutralize or mark it for destruction.
- Inflammation
- A local innate immune response that increases blood flow and brings immune cells to damaged or infected tissue.
- Vaccine
- A preparation that safely exposes the immune system to an antigen so memory cells form without causing the full disease.
- Memory Cell
- A long-lived B cell or T cell that responds rapidly when the same antigen enters the body again.
Common Mistakes to Avoid
- Confusing antibiotics with antivirals is wrong because antibiotics target bacteria, not viruses.
- Saying innate immunity has no recognition is wrong because innate cells recognize broad pathogen patterns, even though they are not antigen-specific like adaptive cells.
- Thinking antibodies directly kill all pathogens is wrong because antibodies mainly neutralize, clump, or label targets for other immune defenses.
- Assuming vaccines give instant immunity is wrong because the body needs time to activate lymphocytes and produce memory cells.
- Mixing up autoimmune disease and immunodeficiency is wrong because autoimmune disease is an immune attack on self, while immunodeficiency is weak or missing immune function.
Practice Questions
- 1 A disease has R0 = 4. Use H = 1 - 1/R0 to estimate the herd immunity threshold.
- 2 If one infected person infects an average of 2.5 people in a fully susceptible population, what is the R0 value?
- 3 A patient receives a vaccine booster and produces antibodies much faster than after the first dose. Which immune cells explain this faster response?
- 4 Explain why a person can have inflammation at a cut before the adaptive immune system has produced specific antibodies.