13. Immunity. Definition. Types of immunity. The protective role of adaptive immunity in the oral cavity. Microbial factors counteracting the mechanisms of adaptive immunity · Microbiology · MU Plovdiv

Immunity, Immunity as a Biological Phenomenon and Types of Immunity

Immunity is the state of an organism having the biological defenses to fight a disease.
It is defined as the ability of multicellular organisms to resist harmful microorganisms from entering it.
Immunity is a complex biological system.
A key function is that the immune system recognises and tolerates self (own body).
It involves both specific and non-specific components.

Also referred to as the non-specific response.
It is the immunity that is quick to respond and is present/active from birth.
Innate immunity is the non-specific, immediate response to pathogens.
It lacks immunologic memory, is short-lasting, and does not improve upon subsequent exposures.
It consists of physical, chemical, molecular, and cellular defences.
Major components include skin and mucous membranes, phagocytic leukocytes (neutrophils and macrophages), specialised lymphocytes (NK cells), and several plasma proteins including proteins of the complement system.
It can distinguish from self and non-self.
The response is rapid and prevents the establishment of infection.
Specific mechanisms include physical barriers, chemical barriers (like lysozymes, pH, lipids, enzymes, complement factors, interferons, acute phase proteins, antimicrobial peptides), normal human flora (microbiota), and cellular factors like phagocytosis, inflammatory response, and fever.

This is the immune system that is pathogen specific, and is not genetically conferred.
It is based on antibodies and specifically reactive T lymphocytes, acquired through immune system stimulation by microbial antigens.
It develops after a latent period of 1-2 weeks.
Immune memory develops, leading to stronger responses in subsequent infections. This secondary response is accelerated and augmented.
It provides long-lasting protection through the development of immune memory.
Adaptive immunity can be broken down into two types: Humoral and Cell mediated.
Humoral immunity is immunity mediated by macromolecules in extracellular fluids (humours). This includes antibodies and complement proteins. It involves the production of antibodies by plasma cells derived from activated B-cells. Humoral immunity protects the body by neutralizing pathogens, facilitating opsonization, activating complement, and preventing pathogen adherence. It is mediated by B cells which produce antibodies. Antibodies can only attack viruses outside of their host cells.
Cell immunity (or Cell-mediated immunity, CMI) involves the immune response that does not involve antigens but rather phagocytes and T-lymphocytes. It involves the actions of phagocytes, T-lymphocytes and the release of specific cytokines in response to an antigen. Cytotoxic T cells (CTLs) recognise viral peptides on infected cell surfaces and induce apoptosis in infected cells.