Hi answerers,

I have a question concerning immunoglobulin G (IgG) subclasses: In
humans, there are IgG1, IgG2, IgG3, and IgG4, of which IgG1 and IgG3
are cytophilic and complement-fixing. In mice, IgG subclasses
unfortunately have a different nomenclature: IgG1, IgG2a, IgG2b, and
IgG3.

My question is: Which murine subclass best corresponds to which human
subclass, taking in account the function (e.g. complement fixation,
recognition by Fc-receptors....), structure,  serum concentration, and
half-life?

Thanks,

Chrigu

You might try an article in the 1988 Annual Reviews in Immunology.
Google Scholar has this excerpt:

"Structure And Function Of Human And Murine Receptors For IgG
JC Unkeless, E Scigliano, VH Freedman - Annual Review of Immunology,
1988 - immunol.annualreviews.org
... order of binding is IgG1 > IgG3 > IgG4 >> IgG2, with a Ka ... IgG1
binding to human
peritoneal macrophages yields ... ADCC by LGL was IgG3 > IgG2a >
IgG2b, with murine ... "

The Annual Reviews site is down for about 4 hours now; but you could
try later to see what the article actually says or if it is available
on-line.

Search strategy in Google Scholar: igg1 igg2 igg3 igg4  igg2a igg2b

I got to the Annual Reviews site this morning. Unfortunately, they
want $20 to get the pdf version. Since I can't tell exactly what it
says without buying it, since the reference is somewhat old, and since
that review may be more complex than a summary, I'd say forget this
one for on-line purposes.

This seems to be the correspondence:

Human IgG1 <-> mouse IgG2a 
   ability to fix complement and bind protein antigens

Human IgG3 <-> mouse IgG2b
   ability to fix complement and bind protein antigens

(From the references I've looked at, I can't say for sure if these two
should be reversed, that is, human IgG1 <-> mouse IgG2b and human IgG3
<-> mouse IgG2a.)

Human IgG2 <-> mouse IgG3
   binding to mast cells

Human IgG4 <-> mouse IgG1
    recognition of carbohydrate epitopes

This is from a 1995 article: "Selective Increases in Antibody Isotypes
and Immunoglobulin G Subclass Responses to Secreted Antigens in
Tuberculosis Patients and Healthy Household Contacts of the Patients."
You can download a pdf version of the article by going to:

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=170229

and clicking on the pdf link to the left.

Here is the relevant quote from the article:

"In the murine system, switching of antibody responses from IgM to one
of the other isotypes is dependent on different cytokines. Gamma
interferon produced by TH1 cells induces IgG2a and IgG3 in vitro (6,
28); interleukin-4 (IL-4) produced by TH2 selectively stimulates IgG1
and IgE (7). The human counterparts of murine IgG subclasses are based
on similarities in biological and functional activities. Murine IgG2a
and IgG2b and human IgG1 and IgG3 share the ability to fix complement
and bind to protein antigens (25). Murine IgG1 and human IgG4 are
considered to be similar because of their property of binding to mast
cells. Murine IgG3 and human IgG2 both recognize predominantly
carbohydrate epitopes." (page 729, top right)

Their reference 25 is 

25. Scott, M. G., D. E. Briles, and M. H. Nahm. 1990. Selective IgG
subclass expression: biologic, clinical and functional aspects, p.
161?183. In F. Shakib (ed.), The human IgG subclasses: molecular
analysis of structure and function. Pergamon Press, Oxford.

I didn't find this book in Google Print.

-----
A different paper also states that both human IgG1 and IgG3 are most
active in complement fixing and that, for mouse, the most active
subclasses are IgG2a and IgG2b.

"As mentioned above human IgG4 is the only human IgG subclass which
does not activate complement and the subclasses IgG1 and 3 are the
most effective [16,30,32,39,40]. For mouse it is the the subclasses
IgG2a and IgG2b which are active with IgG1 and possibly IgG3 being
inactive whilst in rat all four subclasses are active with IgG2b and
IgG1 being the most effective [16,21,34,35]." (bottom of page 7 and
top of page 8)

You can get a pdf version of this article by going to:

http://scholar.google.com/scholar?hl=en&lr=&q=%22igg+effector+mechanisms%22+%22michael+r+clark%22&btnG=Search

and clicking on the "CHEMICAL IMMUNOLOGY" link.

(This paper also has protein sequences, but I don't know whether
detailed comparisons would resolve the above ambiguity.)