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?

  • $\begingroup$ what M stands for in IgM? $\endgroup$
    – Ashwin.N
    Commented Sep 2, 2015 at 17:28
  • $\begingroup$ Have you done any research on your own? Like a Google search? $\endgroup$
    – MattDMo
    Commented Sep 2, 2015 at 19:41
  • 1
    $\begingroup$ Yes but I did not get the full form of M!! $\endgroup$
    – Ashwin.N
    Commented Sep 3, 2015 at 3:38
  • $\begingroup$ The constant region of heavy chains of IgA are called α (alpha) chains so the English translation of the greek alphapet is A. $\endgroup$
    – Tyto alba
    Commented Apr 27, 2017 at 20:45

1 Answer 1


Ig stands for immunoglobulin. The isotype names have various origins. This paper provides an interesting story:

Black CA. 1997. A brief history of the discovery of the immunoglobulins and the origin of the modern immunoglobulin nomenclature. Immunol Cell Biol 75:65-68.

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)
  • $\begingroup$ What is the full form of IgM? $\endgroup$
    – Ashwin.N
    Commented Sep 4, 2015 at 9:33

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