ABSTRACT
The monoclonal antibody (MAb) content of a serum or ascitic fluid can be quantified by a specific antigen-antibody reaction. However, each MAb needs its own standard and if the corresponding antigen is very difficult to produce, it will be impossible to use it for this purpose. In the rat species, the existence of two kappa light chain allotypes can be used for the titration of MAbs. LOU/C rats bear the IgK-la allotype. Hybridomas obtained by fusion of LOU/C lymphoblasts will thus secrete IgK-la immunoglobulins (Igs). They can be produced in congenie rats of the LOU/C.IgK-lb(OKA) strain 1 which are perfectly histocompatible with LOU/C rats (Platteau and Bazin, unpublished results). Bazin et al. 2 developed two mouse MAbs anti-rat IgK-la allotype (MARK-2 and MARK-3) which can be used for the specific and quantitative detection of IgK-la rat Igs in a serum or ascitic fluid also containing IgK-lb Igs. MARK-2 and MARK-3 are not perfectly specific for the IgK-1 a allotype; however, their affinity for IgK-lb is some 250 times lower. In the tests we developed, this specificity problem was circumvented and results are very reproducible as they were controlled with reconstituted ascites, i.e., MAb-free IgK-lb ascites to which a known quantity of IgK-la MAb was added.
