Properdin Pathway

Properdin Pathway

Properdin Pathway

Properdin (L, pro = to prepare. perdo = to destroy) is a normal serum component of euglobulin nature that plays an important role in nonspecific resistance to infection. The properdin pathway of complement activation is a bypass mechanism that does not require C1a, 4, 2 interaction. This pathway can be triggered immunologically by IgA, lgE, IgG and also nonimmunologically by certain complex polysaccharides, gram negative bacterial endotoxins, and cobra venom factors. Activation of the properdin pathway by these materials triggers a series of highly complex reactions. The exact reaction sequence is still not completely understood, but ultimately results in the generation of a proteolytic enzyme which cleaves C3 into C3a and C3b.

C3b deposits on the surface of the original activating particle and then engages C5 and the terminal components (C6,7,S,9) in the normal fashion. The relative biologic significance of the properdin pathway, as compared to the classical pathway, is unclear at this time. 'The pathway may represent a mechanism for the activation of immune defences when sufficient quantities of specific antibody are not available for activation by the classical pathway. The amount of properdin activity in the blood -seem to be directly related to the degree of nonspecific resistance of an animal to numerous types of infection. Injection of properdin-rich serum from animals having high, levels of properdin increase resistance to infection.

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