Page 176 - Veterinary Immunology, 10th Edition

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FIG. 6.12 The clearance of bacteria from the blood (in this case
Escherichia coli from piglets). In the absence of antibodies, bacteria
are slowly and incompletely removed.

Removal of bacteria from the bloodstream is greatly enhanced if

they are opsonized by specific antibodies. If antibodies are absent
or the bacteria possess an antiphagocytic polysaccharide capsule,
the rate of clearance is decreased. Some molecules, such as bacterial
endotoxins, estrogens, and simple lipids, stimulate macrophage
activity and therefore increase the rate of bacterial clearance.

Corticosteroids and other drugs that depress macrophage activity
depress the clearance rate.

Soluble Proteins Given Intravenously

Unless carefully treated, protein molecules in solution tend to
aggregate spontaneously. If such a protein solution is injected
intravenously, neutrophils, monocytes, and macrophages rapidly
remove these protein aggregates. Unaggregated protein molecules

remain in solution and are distributed evenly through the animal's
blood. Small proteins (<60 kDa) also spread throughout the
extravascular tissue fluids. Once distributed, these proteins are
catabolized, resulting in a slow but progressive decline in their

concentration. Within a few days, however, the animal will mount
an immune response against the foreign protein. Antibodies
combine with the antigen; phagocytic cells remove these antigen-

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