Innate and Adaptive Immunity

• Immunity comes in two forms: innate (non-specific) and adaptive (specific, acquired).

Innate Immunity

• This type of immunity is present from birth.
• External barriers include skin, mucus, nose hairs, ear wax/hair, and respiratory tract cilia.
• Chemical barriers include saliva, digestive enzymes, tears from lacrimal glands, stomach acid (plus Lactobacillus), and urine.

Adaptive Immunity

• This type of immunity develops after exposure to an antigen via vaccines or prior illness.

Elements in the Body

• The body contains bacteria, viruses, parasites, and fungi.

Body Odors

• Body odors like halitosis (bad breath), underarm odor, flatulence (gas), and foot odor, are all effects of bacteria.

Components of Innate Immunity

• This includes the inflammatory response, phagocytosis, natural killer cells, and the complement system.

Human Blood Components

• Platelets: Fragments of megakaryocytes.
• Erythrocytes (Red Blood Cells).
• Leukocytes (White Blood Cells):
  • Lymphocytes:
    • Originate in Bone marrow before maturing elsewhere
    • T cells: Mature in the thymus and involved in cell-mediated immunity, directly attacking infected cells.
    • B cells: Mature in the bone marrow and produce antibodies for humoral immunity, fighting pathogens in body fluids.
    • Natural killer (NK) cells: Part of the innate immune system, killing infected or cancerous cells without prior sensitization.
  • Basophils:
    • Originate in bone marrow
    • Release histamine and other mediators during allergic reactions and inflammation; defend against parasites.
  • Neutrophils:
    • Originate in bone marrow
    • The most abundant white blood cell; phagocytes that engulf and destroy bacteria and pathogens, crucial in the acute inflammatory response.
  • Eosinophils:
    • Originate in bone marrow
    • Involved in allergic reactions and defense against parasites; release enzymes that damage parasite cell walls and contribute to inflammation.
  • Monocytes:
    • Originate in bone marrow
    • Migrate into tissues and differentiate into macrophages, which are phagocytes that engulf and destroy pathogens, cellular debris, and dead cells, and present antigens to T cells.
  • Mast cells:
    • Originate in bone marrow (mature in tissues)
    • Reside in tissues, especially connective tissues and mucous membranes; release histamine and other mediators during allergic reactions and inflammation; involved in wound healing and defense against pathogens.
  • There are more red blood cells than any other kind of blood cell.

Red Blood Cells

• They do not have a nucleus (enucleated).
• Produced in bone marrow.
• They circulate for about 115 days.
• Recycled by macrophages in the liver, spleen, and lymph nodes.
• Each hemoglobin carries 4 oxygen molecules.

Internal Defenses: Inflammatory Response

• Step 1: Chemical messengers are released
  • Cytokines (small proteins, ~40 types) send messages to the nervous system.
    • These messages trigger feelings of lethargy, muscle pain, and nausea, and cause an increase in core body temperature (fever).
      • Fever inhibits pathogen growth and speeds up cellular repair.
    • Interferons interfere with viral replication.
    • Interleukins promote hematopoiesis (manufacture of blood cells and blood plasma).
    • Histamines.
  • Step 2: Capillaries near the infected area dilate (redness and heat) and walls become "leaky" (swelling and pain).
  • Step 3: Leukocytes (WBCs) are attracted to the infected area to begin phagocytosis.
    • Neutrophils arrive early to engulf and digest, forming pus.
    • Macrophages are made from monocytes.

Phagocytosis

• Neutrophils are the first responders, the most numerous WBC.
• Monocytes (WBC) become macrophages.
• Metastasis is when undifferentiated cells travel and create tumors.

Natural Killer Cells

• Natural killer cells are lymphocytes involved in innate immunity.
• They attack viruses or cancerous cells, which can be malignant (deadly) or benign (not deadly).
• They act in response to major histocompatibility molecules (MHC), which allow T cells to distinguish self from non-self.
• Natural killer cells induce programmed cell death.

Complement System

• This system complements both the innate and adaptive immune systems, comprising about 20 types of proteins.
• Synthesized in the liver and macrophages in an inactive form.
• Abundant in blood serum, capable of immediate response to infection.
• Attracted to pathogens already tagged by antibodies.
• Marks pathogens for destruction by phagocytic cells.
• Can combine to open pores in microbial cell membranes, leading to lysis (rupture).

Adaptive/Acquired Immunity

• Lymphocytes (B-cells and T-cells) form in red bone marrow; T-cells mature in the thymus, and B cells mature in the red bone marrow.
• Adaptive immunity occurs after exposure to an antigen (pathogen or vaccination).
• It takes days/weeks to become established.
• Includes cell-mediated (T cells) and humoral (B cells + antibodies) responses.
• Involves memory against reinfection via memory cells.
• B-cells and T-cells that bind too strongly to the body’s own tissues are eliminated.
• Specificity of B-cells and T-cells determined genetically, and may be able to produce 1 x 10^18 unique antibodies.
• They migrate to the spleen (lymphoid organ/phagocytic filter) and lymph nodes until needed during an infection.
• Lyme disease is transmitted through deer ticks and has autoimmune effects.

Cell Mediated Immune Response

• Lymphocytes (T-cells):
  • Helper T-cells warn other immune cells about potential pathogens.
  • Cytotoxic T-cells attack and destroy infected cells.
• Unable to recognize pathogens without assistance from dendritic cells (accessory cells) and macrophages (destroy antigen through phagocytosis).

Humoral Immune Response

• Lymphocytes (B-cells):
  • Each B-cell has only one kind of receptor, differing from every other B-cell.
  • Mature in bone marrow before traveling to lymph nodes or lymph organs.
  • Binds an antigen, attaching it to the MHC Class II molecule.
  • MHC Class II-antigen complex triggers TH-cell to release cytokines.
• Cytokines trigger massive B-cell reproduction.
  • Some become plasma cells, making tons of antibodies (up to 100 x 10^6 molecules per hour).
  • Some become memory cells.

Action of Antibodies

• Neutralization - preventing the antigen from binding its target
• Opsonization - tagging a pathogen for destruction by macrophages or neutrophils
• Complement system activation - antibodies activate complement proteins that directly kill pathogens

Immunological Memory

• Primary immune response: Adaptive immune response to an antigen that has never been encountered before.
• Secondary immune response: Memory cells (B- cells + T-cells) activated VERY rapidly upon re-exposure to the same pathogen.

Immune Tolerance

• Allergies are when the body releases histamine in response to allergens.
• Mast cells help the body recognize itself, differentiating from antigens.
• Histamine is a chemical the body releases in response to allergens.
• Anaphylactic shock is the obstruction of airways during a severe allergic reaction.

Immunodeficiencies

• Can be acquired or inherited.
• 350 known rare chronic disorders.
• Bubble boy is an example of severe combined immunodeficiency (SCID).

Active vs Passive Immunity

• Passive:
  • Transfer from mother to fetus via breast milk.
  • Colostrum is the first milk produced by the mother.
  • Immunoglobulins are antibodies.
  • Post-exposure anaphylaxis treatment is used for rabies, tetanus, and hepatitis B.