Overview of Immunity and Microbial Interactions

Innate immunity

Non-specific and immediate immune response.

Acquired (adaptive) immunity

Specific immune response that is slower to develop but has memory.

Physical barriers

Components like skin and mucous membranes that prevent pathogen entry.

Chemical barriers

Substances like lysozyme and stomach acid that inhibit pathogen growth.

Phagocytes

Cells that engulf and digest pathogens.

Complement proteins

Proteins that enhance phagocytosis and lyse pathogens.

B lymphocytes

Cells that produce antibodies as part of the acquired immune response.

T lymphocytes

Cells that include helper and cytotoxic types, involved in acquired immunity.

Granulocytes

White blood cells with granules, including neutrophils, eosinophils, and basophils.

Agranulocytes

White blood cells without granules, including lymphocytes and monocytes.

Basophils

White blood cells that release histamine.

Eosinophils

White blood cells that combat parasites and are involved in allergies.

Monocytes

White blood cells that differentiate into macrophages.

Neutrophils

Main phagocytes in acute infection.

Natural killer (NK) cells

White blood cells that kill abnormal cells directly.

Opsonization

Coating pathogens with molecules that enhance phagocytosis.

MAC (Membrane Attack Complex)

Structure formed by complement proteins that creates pores in membranes of target cells.

Interferon

Substance that inhibits viral replication and is produced by virus-infected cells.

Phagocytosis steps

Chemotaxis → Adherence → Ingestion → Digestion → Exocytosis.

Bacterial capsule role

Prevents phagocytosis.

Signs of inflammation

Redness, heat, swelling, and pain.

Pyrogens

Substances that cause fever by resetting the hypothalamus.

Humoral immunity

Type of acquired immunity better for plasma microorganisms.

Cellular immunity

Type of acquired immunity better for intracellular microorganisms.

Memory cell

Long-lived cell that responds quickly upon re-exposure to antigen.

CD4 cell

Helper T cell.

CD8 cell

Cytotoxic T cell.

Plasma cell

Activated B cell that produces antibodies.

Antigen presenting cell (APC)

Cells like macrophages and dendritic cells that present antigens to T cells.

MHC-I

Molecule on all nucleated cells that presents to CD8 T cells.

MHC-II

Molecule on APCs that presents to CD4 T cells.

Immunoglobulin

Another term for antibody.

Classes of antibodies

IgG, IgA, IgM, IgE, IgD.

Antibody titer

Measurement of antibody level in blood.

Primary vs. secondary immune response

Secondary is faster, stronger, and mainly involves IgG.

HIV

Virus that affects T helper cells and devastates the immune system.

Hypersensitivity types

I: IgE, allergies; II: IgG/IgM, cytotoxic; III: Immune complex; IV: T-cell mediated.

Natural active immunity

Infection

Natural passive immunity

Breastfeeding

Artificial active immunity

Vaccines

Artificial passive immunity

Monoclonal antibodies

ELISA test

Detects specific antigens or antibodies using enzyme-linked antibodies.

Commensalism

One benefits, other unaffected. Example: skin flora.

Mutualism

Both benefit. Example: E. coli in gut.

Parasitism

One benefits, one is harmed. Example: malaria.

Prevalence

Total cases.

Incidence

New cases.

Non-communicable disease example

Tetanus.

Compromised host example

HIV patient. Opportunistic infection: Candidiasis.

Etiology

Cause of disease.

Virulence factor

Traits enhancing pathogenicity.

Virulence factor examples

Exotoxin, endotoxin, enzymes, capsule, M protein, antigenic variation.

Toxemia

Toxins in blood.

Anti-phagocytosis factors

Capsule, M protein.

Acute disease example

Flu.

Chronic disease example

Hepatitis B.

Latent disease example

Herpes.

Primary infection

First infection.

Secondary infection

After primary weakens host.

Communicable disease

Spreads person to person.

Noncommunicable disease

Does not spread.

Stages of disease

Incubation: No symptoms. Prodromal: Early mild symptoms. Illness: Full disease. Decline: Symptoms lessen. Convalescence: Recovery.

Sign vs. symptom

Sign: Observable (rash). Symptom: Felt by patient (pain).

Fomite example

Doorknob.

Animal reservoir examples

Rabies, plague, Lyme disease.

Nosocomial infection

Hospital-acquired. Examples: MRSA, C. difficile.

Direct contact example

Touching.

Indirect contact example

Contaminated object.

Vector transmission example

Mosquito-borne diseases.

Vehicle transmission example

Contaminated food or water.

Endemic

Constant presence (malaria in Africa).

Epidemic

Sudden outbreak (Ebola).

Pandemic example

COVID-19.

Endotoxin

From Gram-negative bacteria, causes fever and shock.

Exotoxin

From Gram-positive and some Gram-negative, highly specific effects.

Large endotoxin release

Septic shock.

Endotoxin vs. exotoxin difference

Endotoxin: Lipid A, less specific. Exotoxin: Protein, very specific.

Erythrogenic toxin

Streptococcus pyogenes — causes scarlet fever, strawberry tongue.

Exfoliatin toxin

Staphylococcus aureus, scalded skin syndrome.

Tetanus toxin

Clostridium tetani — causes muscle spasms.

Chemotherapeutic index

Kills the pathogen and not the host.

Bactericidal

Kills microbes directly.

Bacteriostatic

Prevents microbes from growing.

Inhibition of cell wall

Beta-lactam (penicillin, carbapenems, cephalosporin).

Beta-Lactamase

Attack the beta-Lactam ring; drug becomes ineffective.

Antimycobacterial Antibiotics

Isoniazid and ethambutol used to treat tuberculosis.

Disruption of cell membrane

Polymyxin B.

Disruption of translation

Aminoglycosides (bactericidal), Macrolides/erythromycin (bacteriostatic), Chloramphenicol (aplastic anemia), Clindamycin (pseudomembranous colitis), tetracycline (stains and impair the structure of bone and teeth).

Interference with metabolism

Sulfa drugs (Sulfonamide) - uses (PABA) as a substrate.

Inhibition of nucleic acid synthesis

The Quinolones (inhibits cartilage development in newborns), and Rifampicin is used to treat tuberculosis.

Disk Diffusion Method

The Larger Inhibition Zone, The More Effective Drug.

Antiviral Agents

Block Viral Uncoating - Acyclovir (cold sore/HSV and varicella), AZT (HIV), Tamiflu used to treat influenza (neuraminidase is needed for release of virus and hemagglutinin is required for entering the cell).

Antifungal Agents

Disrupt ergosterol of fungi, Amphotericin B (Polyenes).

Antiprotozoan

Chloroquine for malaria.

Antihelminth

Niclosamide.