Method Description

Complement Fixation:

The immune response of a person to an infection frequently begins with the formation of specific antibody that is capable of combining in vitro with homologous antigen and complement (C'). The complement fixation (CF) test is a 2-stage test based on the ability of antigen-antibody complexes to bind C'. In the first stage, antigen and antibody combine and fix C'. The second stage is an indicator system in which sheep erythrocytes, sensitized by rabbit anti-sheep red cell antibody (hemolysin), are used to demonstrate the presence of unfixed C'. If the patient's serum contains C'-fixing antibody that reacts with the specific antigen (a positive reaction), C' will be fixed and excess C' will not be available to react with and lyse the sensitized sheep erythrocytes. If no antigen-antibody reaction occurs (a negative reaction), C' will be available to lyse the sheep erythrocytes. The CF titer is determined by the greatest dilution of serum (antibody) in which the sheep erythrocytes are not lysed.(Kaufman L, Kovacs JA, Reiss E: Immunomycology. In: Rose NR, de Macario ED, Folds JD, Lane HC, Nakamura RM, eds. Manual of Clinical Laboratory Immunology. 5th ed. ASM Press; 1997:591-592; Pappagianis D, Zimmer BL: Serology of coccidioidomycosis. Clin Microbiol Rev. 1990;3:247-268; Ramanan P, Wengenack NL, Theel ES. Laboratory diagnosis for fungal infections. A review of current and future diagnostic assays. Clin Chest Med. 2017;38[3]:535-554. doi:10.1016/j.ccm.2017.04.013)

Immunodiffusion:

Immunodiffusion (ID) is a qualitative test employed for the detection of precipitating antibodies present in the specimen. Soluble antigens of the fungus are placed in wells of an agarose gel filled Petri dish and the patient's specimen and a control (positive) are placed in adjoining wells. If present, specific precipitate antibody will form precipitin lines between the wells. Their comparison to the control establishes the results. When performing the ID test, only precipitin bands of identity with the reference bands are significant.(Kaufman L, Kovacs JA, Reiss E: Immunomycology. In: Rose NR, de Macario EC, Folds JD, Lane HC, Nakamura RM, eds. Manual of Clinical Laboratory Immunology. 5th ed. ASM Press, 1997:591-593; Ramanan P, Wengenack NL, Theel ES. Laboratory diagnosis for fungal infections. A review of current and future diagnostic assays. Clin Chest Med. 2017;38[3]:535-554)