The germ-line theory was a proposed explanation for

immunoglobulin diversity An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and Viral disease, viruses. The antibody recognizes a unique m ...

that proposed that each

antibody An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...

was encoded in a separate germline gene. This does not occur in most species (including humans), but may occur in

Elasmobranchs Elasmobranchii () is a Class (biology), subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), Batoidea, rays, skate (fish), skates, and sawfish (superorder Batoidea). Members of this subclass are characteris ...

. For decades microbiologists searched for a mechanism that could explain the large diversity of antibody structure. For this reason the germ line theory emerged. According to this theory, the genomes contributed by the germ cell, sperm and egg contained a large repertoire of immunoglobulin genes. It was clear that there should be a mechanism that help the antibody to have diversity and keep it constant. The germ line theory could not provide any explanation on this aspect.

References

Germ line cells Lymphocytes Obsolete immunology theories {{immunology-stub