As requested by the _Therapeutic Gazette_, I shall attempt to describe
as succinctly as possible the theory of the opsonins and the therapeutic
results that have been obtained by the application of the new theory. As
the years go by we realize more thoroughly the correctness of the
prophetic belief of the “Immortal Pasteur,” that the day would come when
it would be possible to eradicate the infectious diseases by
vaccination.
We are indebted to Metchnikoff for calling attention to and explaining
the rôle of the white blood cells in the defence of the body against
bacterial invasion, but the phenomenon of phagocytosis is not so simple
as it at first appeared, as little by little new facts are developed
which amplify our knowledge of the subject.
It was shown by Denys and Leclef, in 1895, that when rabbits were
immunized against _Streptococcus pyogenes_ the serum acquired but slight
bactericidal properties, but that such serum, when brought in contact
with the leucocytes of normal or immunized rabbits, greatly enhanced
their phagocytic activity. Conversely no acceleration of phagocytosis
was observed when the corpuscles were brought in contact with the serum
of a normal animal.
Mennes two years later confirmed this by showing that similar results
were obtained from the blood serum of guinea-pigs treated with cultures
or toxins of Pneumococci.
A method of measuring the phagocytic activity of the leucocytes was
developed by Leishman in 1902. In 1903 Wright and Douglas made an
extensive study of the phagocytes, when brought in contact with
suspensions of _Staphylococcus pyogenes_, and were able to show:
(1) Quoting from the original: “We have here conclusive proof that the
blood fluids modify the bacteria in a manner which renders them a ready
prey to the phagocytes. We may speak of this as an ‘opsonic’ effect
(_opsono_ [a Latin verb], I cater for; I prepare victuals for), and we
may employ the term ‘opsonins’ to designate the elements in the blood
fluids which produce this effect.”
(2) Normal blood serum and plasma possess the same opsonic action upon
bacteria.
(3) Serum loses its opsonic action when heated to 60° C. This is spoken
of as inactivated serum.
(4) Inactivated serum and physiological salt solution have the same
influence upon phagocytosis.
(5) “The opsonic power of the blood fluids disappears gradually on
standing,” losing about 50 per cent. of its activity in five or six
days.
(6) An anti-opsonic effect is noted when blood serum is digested with
typhoid bacilli.
(7) When a condition of immunity is conferred upon patients infected by
Staphylococci, by vaccination with heated cultures of Staphylococci, the
opsonic action of the patient’s blood serum is greatly augmented.
Neufeld and Rimpau (1904) found in antistreptococcic and pneumococcic
sera evidence of substances which, while inactive towards leucocytes,
possessed very marked opsonic or sensitizing action, as they termed it,
toward corresponding cultures of streptococci and pneumococci.
Ross (_Lancet_, November, 1906) summarizes our knowledge of the opsonins
as follows:
“(1) Opsonins act by chemically uniting with the invading bacteria, and
so altering them that the leucocytes are able to phagocyte the bacteria
and destroy them. It is important to remember that these substances do
not stimulate or otherwise affect the leucocytes.
“(2) It is probable that there are present many varieties of opsonins in
the blood plasma, each having to do with combating a particular kind of
microbic invasion.
“(3) Opsonins have been shown to be distinct from other bacteriotropic
substances, such as the bacteriolysins, the agglutinins, and the
antitoxins.”
The leucocytes of healthy or diseased persons seem to be equally active
when brought in contact with the same serum, hence the amount of
opsonins present in the blood of an individual determines, according to
the opsonic theory, his susceptibility to bacterial invasion.