Ans: Granulocytes – polymorphonuclear leucocytes

• Basophils – closely associated with allergic reactions contain heparin, histamine and other substances that promote inflammation.
• Neutrophils – protect against any foreign material that gains entry to the body mainly microbes, and remove waste materials.
• Eosinophils – specialised role in the elimination of parasites, for example, worms. Found at sites of allergic inflammation, for example, asthmatic airway and skin allergies.

Agranulocytes – monocytes and lymphocytes

• Monocytes are large mononuclear cells that originate in red bone marrow – Some circulate in blood, whereas others migrate into tissues and develop into macrophages.
• Both cells produce interleukin 1:
  
  • Acts on the hypothalamus causing the rise in body temperature associated with microbial infections and enhances the production of activated T- lymphocytes.

Ans: Innate immunity is the immunity that we are born with; it reacts to all antigens in the same way.

Defence at body surfaces

• Skin
• Mucous membranes
• Hair in nose – Phagocytosis
• Neutrophils (polymorphonuclear leucocytes) – most important phagocytes. Their granules and lysosome contain degradative enzymes. Attracted by chemicals (chemotaxis) and move towards the area of highest concentration. They engulf the offending cell/particle enclose its membrane and release hydrolytic enzymes. When neutrophils die their contents are released, remnants of their enzymes cause liquification of surrounding tissue. Accumulation of dead neutrophils, tissue and other cell debris for pus (purulent discharge).
• Macrophages (monocytes and mononuclear phagocytes) – remove cell debris as well as attacking bacteria and some fungi. Longer lived than neutrophils as they have a greater glycogen reserve – can replenish lysosomal contents.
• Natural killer – non-specific lethal lymphocytes which have no immunological memory but attack and kill on contact anything which is recognised as foreign or abnormal. They target tumour cells and infectious microbes, particularly viruses. Low NK cells are associated with stress, poor nutrition, overwork, acute or chronic disease, emotional trauma and bereavement. Numbers are reduced in cancer, severe viral infection, AIDS and some autoimmune disorders.

Natural anti-microbial substances

• Hydrochloric acid – in gastric juice, is too acidic for pathogens to survive.
• Lysozyme – small protein with antimicrobial properties in granulocytes, in tears (not present in sweat, urine or CSF).
• Antibodies – in nasal cavities and saliva inactivate microbes.
• Saliva – being slightly acid, is antibacterial.
• Interferons – substances produced by T-lymphocytes and cells that have been invaded by viruses; they prevent viral replication and spread of viruses to healthy cells.
• Complement – a system of about 20 proteins found in blood and tissues that is activated by presence of an antigen and antibody bound together (immune complexes) and by foreign sugars on bacterial cell walls.
• Inflammatory response.

Ans: 

• Redness – from vasodilation due to increased permeability due to the release of histamine and serotonin.
• Heat – in the local area is from increased blood flow to the area; inflammatory response may be accompanied by a rise in core temperature (pyrexia). Pyrexia increases the metabolic rate of cells in the infected area.
• Pain – occurs when local swelling compresses sensory nerve endings. Release of bradykinin.
• Swelling – local oedema due to accumulation of fluid around affected tissues.
• Loss of function – may be experienced due to sudden local oedema.

When a part of the body becomes injured or infected, a number of physiological changes (the so-called ‘triple response’) occur in the affected area:

• Local vasodilation
• Increased permeability of capillaries
• Infiltration of damaged tissues by white cells

Together, these changes constitute the inflammatory response, which brings plasma proteins and leucocytes to the point of injury/inflammation.

If the infection or trauma is sufficiently extensive, the injured tissues become infiltrated by polymorphonuclear leucocytes, particularly neutrophils; once in the tissues, the leucocytes ingest invading organisms.

Ans: This type of immunity is acquired throughout life. It may be cell-mediated (T-lymphocytes) or humoral (B-lymphocytes).

• When antigens are encountered for the first time there is a primary response in which a low level of antibodies can be detected in the blood after approximately two weeks. A second encounter with the antigen produces a secondary response in which there is rapid response by memory B-cells resulting in a marked increase in antibody production.
• May be naturally or artificially acquired.

Ans: Active immunity

Active immunity is acquired in one of two ways:

• Active naturally acquired immunity – the body is stimulated to produce its own antibodies by a) having the disease or b) having a sub-clinical infection.
• Active artificially acquired immunity – develops in response to the administration of dead or artificially weakened microbes (vaccines) or deactivated toxins (toxoids).

Passive immunity

Passive immunity is acquired in one of two ways:

• Passive naturally acquired immunity – acquired before birth by the passage of maternal antibodies across the placenta to the foetus and to the baby in breast milk.
• Passive artificially acquired immunity – ready-made antibodies in human or animal serum are injected into the recipient (immunoglobulins).

Ans: In February each year, the World Health Organization (WHO) assesses the strains of flu virus that are most likely to be circulating during the following winter in the northern hemisphere.

Based on this assessment, the WHO recommends which three flu strains the vaccines should contain for the forthcoming winter. Vaccine manufacturers then produce flu vaccines based on the WHO’s recommendations.

There are three types of flu viruses, which are as follows:

• Type A flu virus, usually the more serious type. The virus is most likely to mutate into a new version that people are not resistant to. The H1N1 (swine flu) strain is a type A virus. Pandemics in the past were type A viruses.
• Type B flu virus generally causes a less severe illness and is responsible for smaller outbreaks. Type B mainly affects young children.
• Type C flu virus usually causes a mild illness similar to the common cold.

The injectable flu vaccine contains three different types of flu virus (usually two A types and one B type). For most vaccines, the three strains of the viruses are grown in hens’ eggs. The viruses are then deactivated and purified before being made into the vaccine.

The vaccine stimulates your body’s immune system to make antibodies to attack the flu virus. If your body is exposed to the strain of virus again a secondary response will occur. Memory B-lymphocytes will produce the antibodies necessary to eradicate the pathogen.