How to choose the best host species for your polyclonal antibody production?

The choice of a host species for custom polyclonal antibody production can be motivated by several criteria:

• The phylogenetic distance between the immunized animal and the antigen donor species: In order to enhance the immune response, the animal host species has to differ from the antigen donor: the higher the phylogenetic distance, the higher the immune response.
• The needed quantity of polyclonal antibodies: Large amounts will often necessitate the use of farm animals, while small amounts can be obtained from traditional lab animals. The quantity of polyclonal antibodies obtained also relies on individual factors, such as the age of the host animal, his size and weight, his gender, his health status and his lifespan.
• Some manageable conditions can also influence the pAbs production. An enriched housing environment, a low stress level and an adapted diet have been shown to improve the quantity and quality of produced antibodies. The housing facilities of the animal and the ease of obtaining blood samples are also considered when it comes to selecting between equivalent host species.

Commonly used species for polyclonal antibody production

Commonly used animal species in the laboratory for polyclonal antibody production are rabbits, rats, mice, guinea pigs, hamsters, goats, chickens, sheep and llamas. The advantages and drawbacks of each one of these hosts will be reviewed below.

Rabbits

Rabbits are the most frequently used animals for the primary immunization step of polyclonal antibody production, as their small size and long life-span make them particularly convenient for housing. Moreover, their strong immune response is well adapted to pAbs production and their blood is quite easy to obtain. This makes pAbs production in rabbits easy and low-priced. However, due to their small size, rabbits produce small amounts of antibodies. This drawback requires the immunization of several animals with the same antigen, in order to obtain a sufficient quantity of serum.

Mice and rats

Mice and rats are often used for monoclonal antibody production, but not that much for polyclonal antibody production because of their small size and associated blood volume.

Guinea pigs

Despite their long phylogenetic distance from humans, guinea pigs share several similarities with us, such as the requirement for a dietary supply of vitamin C, making them particularly interesting for various studies. Moreover, their production yields are twice higher than mice’s and they are well adapted to lab housing conditions. However, guinea pigs are quite difficult to bleed, which make them less likely than rabbits to be used for polyclonal antibody production.

Chickens

Chickens represent a very interesting alternative to rabbits for hosting polyclonal antibody production. Indeed, they produce IgY antibodies, available at high concentrations in egg yolks. These latter can therefore be easily collected directly from the egg, avoiding the invasive bleeding step. This fast and cheap process can generate up to 10 times more antibodies than rabbit blood, due to the continuous secretion of IgY in the eggs. However, several factors limit the use of chickens for pAb production  such as isolation and purification difficulties.

Sheep

The production of sheep polyclonal antibodies is more complicated and expensive than traditional laboratory animals, but allows the production of larger volumes. The resulting antibodies have a high affinity and sensitivity, and are particularly adapted to small antigens or small epitopes.

Goats and horses

Goats and horses are mainly used for polyclonal antibody generation when large quantities of antisera are needed. They offer a low batch-to-batch variation. Moreover, the high phylogenetic distance from rabbits allow double immunostainings.

Camelids

Llamas, alpacas and other camelids are very appreciated for antibody production because of their very interesting properties: indeed, they produce a very particular kind of antibodies referred as VHH antibodies or nanobodies. These single chain antibodies are only composed of two heavy chains and no light chains or CH1 domains. Their small size allows them to reach hardly accessible antigens; they are also more likely to penetrate difficult-to-access tissues.

Summary