What is the exact meaning and full form of IgM, IgG, IgA, etc? What is the rationale behind the names of the isotypes, if there is one? For example, what does "M" mean in IgM?
Ig stands for immunoglobulin. The isotype names have various origins. This paper provides an interesting story:
A brief summary, in order of characterization and naming:
- IgG - named gamma globulin because it migrated in the gamma band of electrophoresed blood plasma (the bands were named in order of mobility: alpha, beta, etc)
- IgM - named macroglobulin because it sedimented faster than IgG (ie was larger)
- IgA - found in the beta and gamma bands of electrophoresed plasma and initially named β2A and γ1A, later renamed to alpha globulin
- IgD - named by process of elimination: IgA was taken, murine immunoglobulins were expected to be named beta, the letter C has no Greek equivalent
- IgE - named because it was most reactive with a fraction of pollen proteins (fraction E because it induced erythema)