May 26, 1944
Dr. J. David Newburgh
3076 Geddes Avenue
Ann Arbor, Michigan
Dear Mr. Newburgh:
I am sorry that you will not be able to come to Pasadena and to take part in our research
program in immunochemistry immediately, and I hope that you will come here after another
year has gone by. I am sure that our program would benefit from your participation
in it.
I shall look forward to hearing about the results of your experiments with the choline
diester of terephthalic acid and Kahn positive sera.
Our experiments continue to give interesting results. We have found that haptens which
are not very closely related to the haptenic group of the immunizing azoprotein often
produce an increase in the amount of precipitate formed by antiserum and a simple
polyhaptenic precipitating antigen. This effect of enhancement of precipitation does
not occur when an azoprotein is used as precipitating antigen. The interpretation
of this phenomenon had us puzzled for some time; not it seems clear that the phenomenon
is the result of the presence in antibody molecules of a cavity into which two haptenic
groups of an antigen can fit. If two haptenic groups of a simple substance fit into
such a cavity, the rest of the substance may not protrude far enough to form a length
with another antibody molecule; a heterologous hapten may, however, itself fill one
of the two parts of the cavity (that part which is less suited to combination with
the haptenic group of the immunizingantigen), leaving the other part of the cavity
free to combine with one haptenic group of the polyhaptenic substance. Presumable
the reason that azoproteins do not show this effect is that the azoprotein molecule
has so many haptenic groups attached that the attachment of two of them to the antibody
does not interfere with combination with other antibody molecultes.
Sincerely yours,
Linus Pauling
LP:Jr
