A new immunoglobulin sub-class in the sheep.

A new immunoglobulin sub-class, IgG1, has been defined in the sheep with the aid of an antibody prepared by immunizing goats with sheep IgG. The sub-class antigen is located on the Fc fragment and is carried by approximately 20 per cent of the IgG1 molecules. IgG1 is lacking in the serum of some sheep and this appears to be under X-linked genetic control. No marked breed distribution was found for IgG1 negativity.