A VHH, a single domain antibody from camelid, first came to light by accident, when during a practical course, a couple of biology students at the Free University of Brussels objected to analyzing human blood for a lab exam because they worried about the possibility of contracting a disease, the samples might be contaminated with HIV. They also refused to kill a mouse to obtain its blood, recalls Serge Muyldermans, a molecular biologist at the university. Some rummaging around, turned up an alternative: a few liters of frozen dromedary camel serum collected to study the animals' parasites were discovered in the lab freezer.
This exotic example inspired the students to start working on the antibody separation.
But another apparent problem cropped up when the students finished analyzing the blood. Along with normal antibodies, they also discovered a group of undersized version of the molecules that did not correspond to anything known to science. "We thought that they had done something wrong," Muyldermans says. So he and other scientists at the university investigated the matter more deeply. An analysis of blood from zoo animals in the same evolutionary family revealed that all had the same diminutive antibodies.
They did not believe that this species were just degraded variants of the “real” antibodies, but started to characterize them in more detail. Eventually, it became clear that they had discovered a new class of antibodies that were naturally devoid of light chains but consisted of two heavy chains attached to variable domains (variable heavy homodimers, VHH), so-called heavy- chain antibodies (HcAb). These antibodies were later found in many. camelid species, including llamas and alpacas. Interesting fact that hcAb has not been found in other organisms, with the curious exception of sharks and other cartilaginous fish (Chondrichthyes), the oldest living beings with an adaptive immune system.