ImmunologyThe Body’s Defenses

Chapter 33

I. How Microbes Cause DiseaseA. pathogen• any disease-causing organism

B. antigens (ag)• any substance that triggers the immune system to respond

C. infections can be superficial or systemic, or one then the otherD. bacteria

1. adherence (with adhesions or fimbriae)2. colonization invasiveness3. toxins: damage to cells/tissues damage to host4. enzymes: increase virulence, degrade cells/tissues, cause/dissolve clots5. capsule: helps resist phagocytosis

E. viruses• replication inside host cells (lytic and lysogenic cycles)

F. fungi1. usually cause superficial infections through enzymes (e.g., keratinase)2. allergic reactions3. toxins

G. protists (protozoa)1. ingest host cells and fluids2. invade rbc’s

H. algae• neurotoxins

I. disease transmission can be direct or indirect

II. Host DefenseA. nonspecific defenses

1. very general (broad spectrum) work on any antigen2. not as strong as specific defenses3. first line

a. anatomical barriersi. intact skin and secretions of skinii. saliva and mucous

b. coughing and sneezing reflexesc. normal flora

i. bacteria normally living in body compete with pathogensii. slow down growth of pathogen or spread of antigen

4. second linea. phagocytic leukocytes (wbc's)

i. neutrophils: release some destructive chemicalsii. eosinophils: defense against larger parasitesiii. monocytes: immature macrophagesiv. macrophages: act as antigen-presenting cells (APC's)v. dendritic cells: act as antigen-presenting cells (APC's)

Fig. 33.5 A macrophage engulfing multiple bacteria

b. other nonspecific leukocytes (not phagocytic)i. basophils: release histamine and heparinii. natural killer (NK) cells: destroy viral-infected and tumor cells

c. antimicrobial substancesi. tears (lysozyme)ii. transferrins• iron-binding proteins in blood• reduce available Fe for pathogen

d. molecular defensesi. interferon• anti-viral protein produced by

infected cells ii. some antitoxins• neutralize toxins

iii. complement system• 20+ proteins in blood• many functions

e. inflammation and feveri. confine infectionii. raise temp. above pathogen’s normal

range

Fig. 33.6 Action of the complement system against bacteria

Fig. 33.3 A summary of nonspecific defenses

B. specific defenses (third line of defense)

1. respond only to one antigen at a time (narrow spectrum)2. stronger than nonspecific defenses 3. specific leukocytes (lymphocytes)

a. T-cellsb. B-cells plasma cells

4. antibodies (immunoglobulins; ab)• proteins that bind specifically (lock-and-key) to antigens (ag)

5. some antitoxinsIII. Specific Immunity

A. kinds of immunity

1. innate: genetics or 1st and 2nd line only2. acquired: some way other than genetics; involves specific defenses

a. active: body makes it’s own ab’si. naturally acquired active: by having a disease ii. artificially acquired active: through vaccine • weakened or dead form of antigen causes immune response

b. passive: body obtains ab’s through external sourcei. naturally acquired passive: across placenta or in breast milkii. artificially acquired passive: through immune serum

B. antigens (ag)

1. usually parts of pathogens • foreign proteins or carbs of certain size

2. haptens and allergens

C. cells and tissues involved in specific immunity1. specific leukocytes (lymphocytes)

a. B-cells produce abi. become plasma cells secrete abii. memory cells protect if invaded by same pathogen again

b. T-cells i. cytotoxic (Tc)• destroy viral-infected, tumor, or foreign cells

ii. helper (Th)

• activate Tc, B-cells, and other immune cells

iii. suppressor (Ts)• turn immune system off after infection

iv. memory (Tm)

• become Tc or Th to protect against same antigen

2. circulatory and lymphatic systemsa. transport immune substances to site of infectionb. leukocytes concentrate and mature in lymph nodesc. immune surveillance • lymph nodes, Tc, macrophages, NK cells

D. four general properties• recognition, specificity, heterogeneity, memory

Fig. 33.14 Action of cytotoxic T-cells

Cytotoxic T-cells attacking and destroying a cancer cell (target cell)

IV. Dual Nature of Immune SystemA. humoral immunity (antibody-mediated)

1. consists of: a. B-cells, plasma cells, memory cellsb. Ab circulating in blood

2. defends against extracellular pathogens and free ag 3. properties and structure of Ab’s

a. heavy vs. light chainsb. constant vs. variable regions

4. classes of Ab’s a. IgGb. IgMc. IgAd. IgEe. IgD

Fig. 33.11 Structure of an antibody

The five classes of antibodies

5. ab’s work by neutralizing an aga. neutralization renders ag ineffectiveb. ways of accomplishing this:

i. coat ag to prevent adherenceii. enhance phagocytosis• coat surface of ag o opsonization

• clump many ag’s together o agglutination

• precipitate soluble antigeniii. act as antitoxinsiv. trigger inflammation and feverv. activate complement system

6. T-cell influence• Th cells bring ag to B-cells activate B-cells ab produced

The action and work of antibodies

B. cell-mediated immunity1. consists of:

a. direct action of T-cells (esp., Th and Tc)

b. nonspecific leukocytes• phagocytic wbc’s, basophils, NK cells

2. defends against intracellular pathogens and cancer 3. process:

a. some macrophages act as antigen-presenting cells (APC's)• bring ag to Th cells Th cells activated

b. Th cells bring ag to B-cells and Tc cells B-cells and Tc cells activated

c. major histocompatibility complex (MHC)• protein on all of an individual’s cells that identifies “self” tissue

C. immune cells communicate with each other through various chemicals

Fig. 33.7 A summary of specific defenses

V. Sequence of Events Occurring During a Typical, First-Time Infection• pathogen (ag) invades and damages body nonspecific defense activate

(2nd line) macrophage phagocytizes a pathogen macrophage displays ag on its surface macrophage presents (APC) ag to a Th cell

Th cell brings ag to B-cells and activates other T-cells (esp., Tc cells) B-

cells produce ab in response to ag some B-cells become plasma cells plasma cells release ab ab’s and various T-cells begin attacking ag some B-cells and T-cells (Th, Tc) become memory cells near end of

infection Ts cells turn immune system off

An overview of the immune response

VI. Immunologic MemoryA. immune system remembers what it has been exposed to previously

1. responds very quickly and efficiently to such ag’s a. memory B-cells become plasma cells release large amts. of abb. memory T-cells (Tm) become Th and Tc cells quickly attack ag

2. most often, symptoms do not even occur

B. primary vs. secondary responseVII. Factors That May Modify the Immune Response

A. compromised hostB. geneticsC. age D. nutritionE. effect of injuryF. environmentG. stress

Fig. 33.9 Primary and secondary response