Innate immunity

Preformed, intrinsic immunity, can function immediately upon entry of the microorganisms
Consists of complement, interferons, skin and mucosa, macrophages, neutrophils and natural killer or NK cells
Nonspecific
No memory
Does not improve after exposure
Main role is to kill invading microbes and to activate adaptive immune responses. * Neutrophil does only the first role while macrophages and dendritic cells perform both roles.
Recognizes foreign antigens by receptors called Pattern Recognition Receptors that recognize a molecular pattern called Pathogen Associated Molecular Pattern (PAMP) , which is not present on human cells

Endotoxin and immune system: Toll like Receptors (TLR) is 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 enhance 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 macrophage called CD14. LPS stimulates a pattern recognition receptor TLR 4 which then transmits a signal to the nucleus inducing 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 causes septic or endotoxic shock.

Vaccine types

Vaccine type	Description	Examples
Live attenuated	Uses an attenuated or weakened strain of the microorganism Stimulates cell mediated, long lasting immunity Temperature sensitive Contraindicated in immunocompromised individuals like HIV, organ transplant recipients etc.	MMR Rotavirus Smallpox Chickenpox Yellow fever Nasal influenza Oral polio (Sabin)
Inactivated	Use 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	Use antigenic parts or 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 like aluminium 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, 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.