4 Immunology : 5 Infection Flashcards by Ryan Bird

What do helper T-cells (CD4) release?

IL2, IL4

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Interleukin that causes maturation of cytotoxic T cells?

IL-2

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Interleukin that causes B-cells maturation into Plasma cells?

IL-4

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Which cells are involved in delayed hypersensitivity reactions?

Helper T-cells (CD4)

Brings in inflammatory cells by chemokine secretions (Type 4 hypersensitivity)

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What cells regulate CD4 and CD8 cells?

Suppressor T-cells (CD8)

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What recognizes and attacks non-self-antigens attached to MHC class I receptors?

Cytotoic T-cells (CD8)

I.e. viral gene products

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How do you test cell-mediated immunity?

Intradermal skin test (i.e. TB test)

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What infections are associated with defects in cell-mediated immunity?

Intracellular pathogesn (TB, viruses)

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Characteristics of MHC class I (A, B, C)

CD8 activation (suppressor, cytotoxic)
Present on ALL nucleated cells
Single chain with 5 domains
Target for cytotoxic T-cells (binds T-cell receptors)

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Characteristics of MHC class II (DR, DP, DQ)

CD4 cell activation (helper)
Present on antigen-presenting cells (i.e. monocytes, dendrites)
2 chains with 4 domains each
Activates helper T-cells (binds T-cell receptor)
Stimulates antibody formation after interaction with B-cell surface IgM

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Effect of viral infection on immune response?

Endogenous viral proteins are produced
Bound to class I MHC
Go to cell surface
Recognized by CD8 cytotoxic T-cells

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Effect of bacterial infection on immune response?

Endocytosis
Proteins get bound to class II MHC molecules
Go to cell surface
Recognized by CD4 helper T-cell

B-cells that are already bound to the antigen are then activated by CD4 helper T-cells
They produce the antibody to that antigen and are transformed to plasma cells and memory B-cells

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Characteristics of natural killer cells

Not restricted by MHC, do not require previous exposure, do not require antigen presentation
Not considered T or B cells
Recognize cells that lack self-MHC
Part of the body’s natural immunosurveillance for cancer

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IgM

Initial antibody made after exposure to antigen
Larges antibody (5 domains, 10 binding sites)

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IgG

Most abundant antibody in body
Responsible for secondary immune response
Can cross the placenta and provides protection in newborn period

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T-cell and B-cell activation?

Two signals are required
First - alloantigen binds to antigen-specific receptors (TCR - T-cells; surface IgM - B-cells)
Second - costimulation via IL-1 (released by antigen-presenting cells)

CD4 helper T-cells release IL-2, IL-4, which provide help for CD8 t-cells and B-cell activation

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How are endogenously synthesized or intracellular proteins processed?

Degraded into peptides, transported to the ER
Bind to class I MHC molecules and are transported to the surface of the antigen-presenting cells
CD8 cells recognize the foreign peptide bound to Class I MHC via TCR complex

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How are exogenous antigens processed?

Endocytosed and broken down into peptide fragments in endosomes
Class II MHC molecules are transported to the endosome, bind the peptide and are delivered to the surface of the antigen-presenting cell, where they are recognized by CD4 cells

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IgA

Found in secretions
In Peyer’s patches in gut
In breast milk
Help prevents microbial adherence and invasion in gut

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IgD

Membrane-bound receptor on B-cells

Serves as an antigen receptor

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IgE

Allergic reactions

Parasite infections

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Which immunoglobulins are osponins?

Makes antigen for immune response

IgM, IgG

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Which immunoglobulins can fix complement?

IgM (1) or IgG (2 needed)

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What is the role of the variable region?

Antigen recogniztion

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What is the role of the constant region?

Recognized by PMNs and Macrophages

Type I hypersensitivity reaction?

Immediate hypersensitivity reaction (allergic) Eosinophils with IgE receptors - release major basic program --> activates mast cells and basophils --> release histamine, serotonin, bradykinin (Bee stings, peanuts, hay fever)

Type II hypersensitivity reaction?

IgG or IgM reacts with cell-bound antigen | ABO blood incompatibility, Graves disease, myasthenia gravis

Type III hypersensitivity reaction?

Immune complex deposition | Serum sickness, SLE

Type IV hypersensitivity reaction?

Delayed-type hypersensitivity Antigen stimulation of previously sensitized T-cells (TB skin test, contact dermatitis)

Major source of histamine in blood?

Basophils

Major source of histamine in tissues?

Mast cells

Primary lymphoid organs?

Liver, bone, thymus

Secondary lymphoid organs?

Spleen, lymph nodes

Function of IL-2?

Converts lymphocytes to lymphokine-activated killer cells (LAK) by enhancing their immune response to tumor Converts lymphocytes into tumor-infiltrating lymphocytes Helpful in melanoma

Tetanus prophylaxis? Non-tetanus-prone wounds

Give tetanus toxoid only if patient has received <3 doses or tetanus status is unknown

Tetanus prophylaxis? Tetanus-prone wounds

(>6 hours old, obvious contamination, devitalization; crush, frostbite, burn or missile injuries) Always give tetanus toxoid

When do you give tetanus immune globulin?

Tetanus-prone wounds in patients who have not been immunized or if immunization status is unknown

Microflora of the stomach?

Virtually sterile | Some GPCs, some yeast

Microflora of the proximal small bowel?

10^5 bacteria | Mostly GPCs

Microflora of the distal small bowel?

10^7 bacteria | GPCs, GPRs, GNRs

Microflora of the colon?

10^11 bacteria | Almost all anerobes, some GNRs, GPCs

Most common anaerobe in colon?

Bacteroides fragilis

Most common aerobic bacteria in the colon?

Escherichia coli

Most common source of fever within 48 hours post-op?

Atelectasis

Most common source of fever within 48 hours - 5 days post-op?

Urinary tract infection

Most common source of fever > 5 days post-op?

Wound infection

Most common cause of gram negative sepsis?

E. coli

E. coli endotoxin - characteristics?

Lipopolysaccharide lipid A | Triggers release of TNF-a from macrophages, activates complement, activates coagulation cascade

Response of insulin and glucose to gram-negative sepsis?

Early - decreased insulin, increased glucose (impaired utilization) Late - increased insulin, increased glucose (insulin resistance)

Optimal glucose level in a septic patient?

100-120mg/dL

When do abscesses occur post-operative?

7-10 days

When do you give antibiotics for abscesses?

Patients with diabetes, cellulitis, clinical signs of sepsis, fever, elevated WBC or bioprosthetic hardware

Risk of surgical site infection in clean cases? (i.e. hernia)

Risk of surgical site infection in clean contaminated cases? (i.e. elective colon resection in prepped bowel)

3-5%

Risk of surgical site infection in contaminated cases? (GSW to colon with repair)

5-10%

Risk of surgical site infection in gross contamination cases? (Abscess)

30%

Why do we give prophylactic antibiotics? When do we stop them?

To prevent surgical site infections | Stop within 24 hours of end of operation (48hrs for cardiac cases)

Most common organism in surgical wound infections?

Staphylococcus aureus (coagulase-positive)

Coagulase-negative gram positive cocci

Staphylococcus epidermidis

Most common GNR in surgical wound infections?

E. coli

Most common anerobe in surgical wound infections?

B. fragilis | Indicates necrosis or abscess - cannot survive in oxygenated tissue

Number of bacteria required for a wound infection?

> 10^5 bacteria (less if there is hardware)

Risk factors for wound infection?

``` Long operation Hematoma or seroma formation Advanced age Chronic disease (i.e. COPD, renal failure, liver failure, DM) Malnutrition Immunosuppresive drugs ```

Causes of surgical infections within 24 hours post-op?

Injury to bowel with leak | Invasive soft tissue infection (C. perfringes, B-hemolytic strep)

Most common infection in surgical patients?

Urinary tract infections Secondary to foleys Most commonly E. coli

Leading cause of infectious death after surgery?

Nosocomial pneumonia | Related to length of intubation and aspiration

Most common organisms in ICU pneumonia?

S. aureus | Pseudomonas

Causes of line infections?

S. epidermidis S. aureus Yeast

Causes of necrotizing soft tissue infections?

Beta-hemolytic streptococcus C. perfringens Mixed organism

Findings of necrotizing soft tissue infections?

``` Pain out of proportion to skin findings WBCs >20 Thin gray drainage Can have skin blistering/necrosis Induration and edema Creptus or soft tissue gas on x-ray Can be septic ```

Treatment of necrotizing fasciitis?

Early debridement | High-dose penicillin

When do you need fungal coverage?

``` Positive blood cultures 2 sites other than blood 1 site with severe symptoms Endophthalmitis Patient on prolonged antibiotics with no improvement ```

Characteristics and treatment: Actinomyces?

Pulmonary symptoms most common; causes abscesses | Drainage and penicillin G

Characteristics and treatment: Nocardia?

Pulmonary and CNS symptoms | Drainage and sulfonamides (bactrim)

Characteristics and treatment: Candida?

Inhabits the respiratory tract | Fluconazole, anidulafungin for severe infections

Characteristics and treatment: Aspergillosis?

Voriconazole for severe infections

Characteristics and treatment: Histoplasmosis?

Pulmonary symptoms; MIssissippi and Ohio River valley | Liposomal amphotericin for severe infections

Characteristics and treatment: Cryptococcus?

CNS symptoms, AIDS patients | Liposomal amphotericin for severe infections

Characteristics and treatment: Coccidioidomycosis?

Pulmonary symptoms; Southwest | Liposomal amphotericin for severe infections

HIV exposure risk: blood transfusion?

70%

HIV exposure risk: infant from positive mother?

10%

HIV exposure risk: needle stick from positive patient?

0.3%

HIV exposure risk: Mucous membrane exposure?

0.1%

Medications to decrease seroconversion after exposure?

AZT (zidovudine, reverse transcriptase inhibitor), ritonavir (protease inhibitor)

Upper GI bleed in HIV patient?

Kaposi's sarcoma* | Lymphoma

Lower GI bleed in HIV patient?

CMV* Bacterial HSV

CD4 counts and associated symptoms?

800-1200 normal 300-400 symptomatic disease <200 opportunistic infections

Brown recluse spider bites

Treat with dapsone, may need to resect and then skin graft

Acute septic arthritis

Gonococcus, staph, H. influenzae, strep | Treat with drainage, 3rd-gen cephalosporins, vanco

Diabetic foot infection

Mixed staph, strep, GNRs, anaerobes | Broad-spectrum antibiotics (Unasyn)

Eikenella

Only found in human bites - can cause permanent joint injury | Treat with Augmentin

Pasteurella multocida

Found in cat and dog bites | Treat with Augmentin