At last, some antigens from origins other than mouse or rat species can induce much stronger immune responses in rats than in mice and evidently the reciprocal could be true for other antigens. The second reason relates to physicochemical and biological properties of rat immunoglobulins which do not seem to exist in the mouse species. Rat antibodies of the IgG1, IgG2a, and IgG2b isotypes can easily fix the human or the rabbit complement. Likewise, the rat IgG2b antibodies can be efficiently used by human K cells to kill their target cells. The third reason is linked to the in vivo production of rat MAbs.
Rats are approximately ten times bigger than mice.
Although the future of the production of MAbs lies in in vitro culture, at the present time, MAbs in vivo production is less animal cosuming in rats than in mice. However, conventional purification techniques of rat immunoglobulins can also be used, but these techniques are based on properties of heterogenous molecule populations which are rarely found in a given MAb preparation. Techniques of DEAE chromatography, gel filtration, or preparative electrophoresis can be used, but the degree of purity and the percentage of recovery achieved by them are limited. In most cases, affinity chromatography is preferable. However, obtaining rat-rat hybridomas still seems to be considered difficult.