Serology

Immunology

Serology: is the science dealing with the study of antigen–antibody reaction.

Uses:
1- Diagnosis of infections.
2- Evaluation of the immunological status.
Antigen – Antibody Reaction:
Reaction of antigens and antibodies are highly specific. An antigen will react only with antibodies elicited by itself or by a closely related antigen.
Because of the great specificity, reactions between antigens and antibodies are suitable for identifying one by using the other. This is the basis of serologic reactions.
Antigens + Antibodies = product

Types of diagnostic tests:
1. Agglutination test: This reaction can be done in a small cup or tube or with a drop on a slide.
One very commonly used agglutination test is the test that determines a persons’ ABO blood group and the bacterial agglutination tests including Widal and Brucella test (Rose Bengal Test).
Widal test:
Is a presumptive serological test for enteric fever. In case of salmonella infections, it is a demonstration of agglutinating antibodies against antigen O-somatic and H-flagellar in the blood. The test is not
a very specific test, since patients are often exposed to other bacteria (ex. Salmonella enteritidis, S. typhimurium and some types of E. coli).

Procedure:
Patient’s serum is diluted with normal saline by tenth-double dilution by mixing and transferring from 1:10 to 1:640 (serum:normal saline) in three-four rows. Somatic S. typhi O antigen is added to the first row of tubes. For all the remaining rows, different flagellar H antigens are added. Each tube must contain (0.5 ml) of diluted serum. A test tube with only saline is kept in each row as a negative control. All the tubes (including control) in a row are mixed with (0.5 ml) of antigen suspension.