Antigenic structures: Pneumococcus
Antigenic structures: Pneumococcus possesses a number of antigens.
(a) Nucleoprotein: It is neither species specific nor type specific. Antibody to this antigen is not protective.
(b) Species specific polysaccharides hapten: It is situated at the cell surface and is not related with capsular antigen.
(c) Capsular polysaccharide is found in capsulated form. It determines type specificity of organism and virulence. Pneumococci isolated from lobar pneumonia are classified into 4 types: I, II, III and heterogenous group IV. Members of group iv are further classified into various types. Now about 84 types are known named 1, 2, 3 etc.
Typing may be carried out by:
(1) Agglutination of cocci with type specific antiserum.
(2) Precipitation of capsular polysaccharides with specific serum.
(3) Capsular swelling reaction (Quellung reaction): Here suspension of pneumococci is mixed with type specific antiserum. In presence of homologous antiserum the capsule becomes apparently swollen, delineated and refractile.
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