The JMH blood group was first identified by autoantibodies usually found in elderly
men whose red cells exhibited a positive direct antiglobulin test. When found in
women they too were elderly and were often cat owners; hence the earlier nicknames of
this collection of specificities was "The Boys" and "Cat". The name was eventually
assigned based upon the initials of one of the most thoroughly investigated propositi.
Only one family to date has been shown to have an inherited JMH negative phenotype while
the majority of the JMH negatives are due to an acquired suppression of the antigen. As
with many of the early reports, anti-JMH was believed to be a single specificity.
However, the Meged serum (and later others) showed that other polymorphic determinants
were involved in the JMH phenotype.
The JMH antigen is a 76 kD protein as identified by both human and monoclonal antibodies.
In addition to being found on red cells it is also present on leukocytes and it has been
given the cluster determination CDw108. This protein is known to be acquired during lymphocyte
activation and may play a role in cell adhesion. Since it is a GPI-anchored protein, the
JMH antigens are absent from PNH red blood cells as are some of the other blood group bearing
molecules, eg. decay accelerating factor (Cromer).