Specific Defenses Of Host

Immunology NON SPECILIC DELENSES of HOST HOST-PARASITE RELATIONSHIP Any decrease in host resistance or increase in virulence of the microorganism can result in the development of disease because of imbalance in host parasite relationship that had previously been innocuous. Host-parasite interaction is a dynamic equilibrium. When host resistance is impaired, organisms that are even normally present may cause disease. RESISTANCE There are a variety of mechanisms by which human beings resist attack by microorganisms. These can be broadly divided into: · Natural resistance, (innate immunity, nonspecific resistance, or constitutive immunity). · Acquired immunity, (specific, inducible, or adaptive immunity). Natural or innate resistance for host protection develops during ontogeny without contact with any parasite or its products and is not specific for any particular parasite. Inducible mechanisms are only developed following exposure to a particular parasite or its products and are specific for the inducing parasite. Types of host defenses Type of defense Nonspecific immune response Specific immune response

Type of system Physical barriers; skin, cilia, and flushing action, Physiological barriers; inflammation, fever, phagocytes, lymphokines Specific immune system; lymphoid system, immune response, antibodies, cellmediated immunity

Natural Resistance (Constitutive Immunity) Natural resistance or innate immunity refers to that type of resistance which each individual has by virtue of being the individual he or she is in terms of species, race, sex or other factors associated with genetically controlled resistance. Important factors influencing effectiveness of natural resistance are: Species: A given pathogenic organism is often capable of producing disease in one animal species but not in another. Humans get mumps, but dogs and cats do not; mammals may contract anthrax, but birds do not. Racial or Genetic Basis: Within one animal species there may be marked racial and genetic differences in susceptibility. Blacks appear to be more susceptible than whites to tuberculosis. Nutrition: Low protein diets make a person more susceptible to infections. Vitamin deficiencies often exhibit significant effects on host defense. Vitamin A and vitamin C deficiencies are well known to increase susceptibility to bacterial infections. Similarly deficiency of zinc and folic acid predisposes to some infections. Hormone Related: Hormone imbalance (such as in diabetes mellitus, pregnancy) has a direct effect on susceptibility to a number of infectious diseases. Miscellaneous: The age of an individual also has a marked effect on innate immunity. The very young and the very aged always have more infectious diseases than the middle aged groups, possibly because of less phagocytic activity. Likewise fatigue, climate, including simple climatic variation and numerous other factors can significantly alter host resistance. Mechanism of Natural Resistance It operates nonspecifically during the early phase of an immune response. It functions through

activation of nonspecific cells which are phagocytic cells of the mononuclear and granulocytic systems and natural killer (NK) cells. The most significant phagocytic cells are the macrophages and large granular lymphocytes (LGL). Components of natural resistance -External defense systems (first line of defense against infection) · The skin · The respiratory tract · The mouth · The digestive tract · The urogenital tract · The eye -Internal defense systems · Phagocytic cells · Chemotaxis · Phagocytosis · Opsonization · Ingestion · Oxygen dependent killing of microbes · Oxygen independent killing of microbes · Destruction of ingested microbes -Inflammatory response · Local · Generalised Characteristics of Components of Natural Resistance The components of natural resistance are: -Preformed : components that are present before challenge -Standardized : the response magnitude is consistent -Without memory : the host does not realise that it has been re-exposed to same antigen -Nonspecific : it does not differentiate between invaders. Phagocytic cells: The major phagocytic cells are the neutrophils and the monocytes of the blood and the monocytes and the macrophages in the tissues. The neutrophils also may enter tissues as part of the inflammatory response. Opsonization: Opsonins are the substances in the serum that coat organisms and cause them to be engulfed by phagocytic cells (opsonization). After attachment of an opsonized particle to the phagocyte, the phagocyte will surround the particle by forming pseudopods (Fig. 13.2). The killing of ingested microbes and the destruction of ingested material is carried out by a variety of enzymes which are similar to enzymes of digestive tract and are generally present in lysosome of phagocytes.

Some Important nonspecific antimicrobial factors Antimicrobial Chemical Source factor

Effects

Peroxidase(per oxidase Protein enzymes)

Leukocytes, saliva and other sources of peroxidases

Destroys bacterial cell wall also within phagocytes Attacks cytoplasmic membrane; active against Gram-positive bacteria Kills a variety of microorganisms important killing mechanism in saliva and within neutrophils

Interferon

Leukocytes and tissue cells

Interferes with the multiplication of viruses by

Lysozyme

Protein

Most body fluids

Beta-lysin

Protein

Serum leukocytes

Protein

Complement system

Many distinct proteins

causing the formation of antiviral protein. Proteins acting in special Produced by sequence to produce effects macrophages and other such as chemotaxis , host cells opsonization, and cell lysis

Inflammatory Response Inflammation is a complex series of events that is a part of the response of all multi-cellular organisms to the introduction into their tissues of living and nonliving foreign agents. The five cardinal signs of acute inflammation are redness, or erythema; swelling; pain; heat and loss of function. Vasodilatation causes heat and erythema. Exudation by blood plasma and leukocytes causes swelling. Pressure on nerve endings in swollen tissue and the effects of some prostaglandins causes pain. Loss of function may result from buildup of extravascular fluids and cells at the inflammed site. Function may also be restricted as a result of pain. Systemic effects of inflammation Followings are systemic effects of inflammation: · Induction of fever. . Stimulation of production of a group of substances termed colony stimulating factor (CSF), that stimulate the production of granulocytes and monocytes from bone marrow precursor cells. . Induction of acute phase reactants which are a group of plasma proteins that serve as nonspecific host resistance factors and may also function to aid tissue repair. Some of these are C3, alpha Iantitrypsin,alpha l-antichymotrypsin, hepatoglobulin, transferrin, fibrinogen and C-reactive protein.