The macroscopic signs of inflammation at the site of parasite invasion are erythema
(redness), swelling, pain, heat: all related to alterations in microcirculation and the
change in permeability of the walls of epithelial cells.
Vasoactive hormones such as prostaglandins (PGE) and leukotrienes (LT) are released
by the mast cells into the surrounding tissues. These are lipid hormones derived from
arachidonic acid, a compound that originates by the action of phospholipase on the mem-
brane phospholipids. Any substance that damages cell membranes activates the phospholipase.
n The major prostaglandins are PGE1, PGE2, PGE2a, and thromboxane A2. The
prostaglandins were first isolated from seminal fluid produced by the prostrate gland
and they are produced by most cells including phagocytic white blood cells.
n The leukotrienes — include LTB4, LTC4, LTE4 and LTF4 and are derived from
white blood cells (leukocytes).The pain associated with inflammation:n is due partly to swelling, the influx of fluids causing pressure on the local nerve
endings;
n and also to direct action from vasoactive amines such as histamine, serotonin and
bradykinin.The precursors to those compounds are located in the mast cell granules (see sec-
tion 5.6.4) and are released when the mast cells are stimulated to degranulate. These amines
act together with (synergistically) with prostaglandins and this induces pain. Pain acts as
a signal to the system that there is damage and that the area needs some protecting.
In addition to what has just been described, more than one blood protein system is
activated by injury or infection. Once a precursor of these blood proteins is activated they
set off a series of chemical reactions known as a chemical cascade and the reactions gen-
erate soluble mediators of inflammation. The purpose of the cascade is to amplify the local
response and to initiate the subsequent events that occur away from the site.
Specific plasma proteins involved in the chemical cascades associated with inflamma-
tion include kinins, the complement systems, the clotting and the fibrinolytic systems.
The first of the blood plasma proteins to be activated is known as the Hageman Factor
(HFa) which is the first component factor (Factor XII) of the clotting system. Activated
HFa stimulates the kinin and fibrinolytic systems.
Collagen, a chemical compound commonly found in all higher animals, forms a
matrix in which all body cells are embedded and when tissue is damaged the Hageman
factor is activated and binds to the collagen in the damaged tissue. For the healing or resolv-
ing process to proceed the resultant clot must be dissolved. This is achieved by the enzy-
matic activities of plasmin. As the fibrin network is slowly degraded the phagocytic cells
attack any trapped microbes. As the clot disappears it is replaced by scar tissue. The scar
tissue is formed by fibre type cells and deposits of elastin and collagen.
About 10% of the globulin fraction of blood serum is made up of a multicompon-
ent system known as complement, consisting of enzymes and binding proteins. Once
activated the complement cascade generates mediators of inflammation and some of
these are distinct and others are identical to other systems involved. Complement
can be activated directly by a microbe — the alternate pathway — or via the immune
system — the classical pathway. The end from either pathway is the accumulation of cells
associated with inflammation and phagocytosis.
PATHOLOGICAL EFFECT OF THE PARASITE UPON THE HOST