"The Evolution of Complement and the Alternative Pathway."
I am Peter Lachmann, Emeritus Sheila Joan Smith,
Professor of Immunology in the University of Cambridge.
There are two ways to look at complement evolutionary history.
The first is to look at the sequence in which complement was discovered,
and that starts from the classical pathway,
long before the alternative pathway.
On the other hand, one can look at the evolutionary history,
and that is different starting from the alternative pathway,
and the classical pathway,
being evolutionary, restricted to its vertebrates.
That goes back to the late 19th century,
when a number of workers,
von Fodor, Nuttall, Buchner,
observed bactericidal activity in normal serum.
In 1894, Pfeiffer and Issaeff
showed that you could lysis Vibrio Cholerae in the peritoneum
of immune guinea pigs and also
normal guinea pigs when they are given antibodies intraperitoneally.
But the real discoverer of complements is Bordet in Belgium,
who showed that when you add
normal serum to a mixture of Vibrios and heated immune serum,
this gives you lysis in vitro.
He then went on to show,
as well as Ehrlich and Morgenroth similarly showed,
that erythrocytes in the presence of antibody can
be lysed by normal serum containing complement.
He called it alexine.
Ehrlich called it complement.
The critical experiment was done in 1901,
when Bordet and Gengou described complement fixation,
thereby showing for the first time that complement is not just an activity,
it was actually a substance.