Innate immunity

• Preformed (intrinsic) immunity that can function immediately when microorganisms enter the body
• Consists of complement, interferons, skin and mucosa, macrophages, neutrophils, and natural killer (NK) cells
• Nonspecific
• No memory
• Does not improve after exposure
• Main role is to kill invading microbes and activate adaptive immune responses. * Neutrophils do only the first role, while macrophages and dendritic cells perform both roles.
• Recognizes foreign antigens using receptors called pattern recognition receptors (PRRs). PRRs recognize molecular patterns called pathogen-associated molecular patterns (PAMPs), which are not present on human cells.

Endotoxin and immune system: Toll-like receptors (TLRs) are a family of receptors found mainly on the surface of macrophages, dendritic cells, and mast cells. TLRs recognize various microbial components and then activate transcription factors that increase the synthesis of several proinflammatory cytokines.

Endotoxin (LPS/Lipid A), when released from the bacterial (gram-negative) cell surface, combines with LPS-binding protein, a normal component of plasma. This protein then transfers LPS to a receptor on the surface of macrophages called CD14. LPS stimulates the pattern recognition receptor TLR4, which transmits a signal to the nucleus and induces the production of cytokines IL-1, IL-6, IL-8, and TNF. It also stimulates the costimulatory protein B7, which is required to activate helper T cells and produce antibodies. This can cause septic (endotoxic) shock.

Vaccine types

Vaccine type	Description	Examples
Live attenuated	Uses an attenuated (weakened) strain of the microorganism Stimulates cell-mediated, long-lasting immunity Temperature sensitive Contraindicated in immunocompromised individuals (e.g., HIV, organ transplant recipients)	MMR Rotavirus Smallpox Chickenpox Yellow fever Nasal influenza Oral polio (Sabin)
Inactivated	Uses killed microorganisms Booster doses are essential for long-lasting immunity	Hepatitis A Flu shots Polio shots (IPV or Salk) Rabies
Subunit, recombinant, polysaccharide and conjugate	Uses antigenic parts (subunits) of the pathogen to induce specific immunity Booster doses are required	Haemophilus influenzae type b or Hib Hepatitis B HPV Pertussis component of DTaP Pneumococcal Meningococcal Shingles
Toxoid	Uses inactivated toxins	Diphtheria and Tetanus

Adjuvants are added to some vaccines to increase immunogenicity (e.g., aluminium added to tetanus toxoid; pertussis toxin in DTaP). Toxoids are inactivated toxins that are not toxic but are still immunogenic.

Vaccine adverse effects include fever, local erythema, and swelling after DTaP booster doses, and allergic reactions to neomycin in MMR, IPV, and chickenpox vaccines. Influenza vaccine is contraindicated in egg allergies. Thiomersal is a mercury-containing preservative used in vaccines and can be potentially toxic to the developing brain of infants.