Læknablaðið : fylgirit - 01.05.1978, Blaðsíða 127

Hans - E. Kallerup
Department of Rheumatology, University of Aarhus,
Aarhus Kommunehospital, Denmark
Specificity oí the method. Occurrence of IgG-
rheumatoid factor in serum from seropositive
and seronegative rheumatoid patients, and in
controlsera.
It has been suggested to classify Rheumatoid
Arthritis (RA) according to the local presence oí
IgG-IgG complexes, which may play a possible
role in the pathogenesis of the disease (4), and
which in some instances have been shown to
possess IgG-rheumatoid factor (IgG-RF) activity.
On this background measurement of IgG-RF in
serum from RA patients probably would be of
interest. To do this immunosorbents technique
has been used (7,12) but this technique has been
critizised because of the possibility of unspecific
reactions (13,14) and furthermore it is time
consuming.
This paper deals with a modified indirect
immunofluorescence technique (IF-test) used for
the demonstration of IgG-RF in serum. The
specificity of the method and its application on
a limited clinical material will be discussed.
The methoa and its sensitivity:
The method is based on the principle of the
Waaler-Rose test, and is a modification of a
work published by Johnson 1963 (3) and Atra
1972 (1). It will be briefly summarized:
Formalinfixed sheeperythrocytes are smeared or
a glass slide and sensitized with rabbit-anti-
sheeperythrocyte-IgG (amboceptor). Patient
serum is applicated on the slide in a suitable
dilution. Possible rheumatoid faetors (RF)
present in the serum may react with the
amboceptor, and can be detected by using
fluorescin-isothiocyanatt (FITC) labelled mono-
specific antihuman IgG, IgM or IgA serum. The
slides are read in a microscope equipped with
UV-light (filter combination 4mmBG12, 3mm
BG38, KP490, TK495 and K510). Known positive
and negative controls and control of the testsystem
are included, and each serum is tested parallel
with a slide without amboceptor - this slide has
to be negative.
By this method sera from 54 patients with
definite RA, and 20 healthy blood donors were
DETECTION OF IGG AND IGM
RHEUMATOID FACTORS WITH
A MODIFIED INDIRECT IMM-
UNOFLUORESCENCE METHOD
mvcstigated. Scra wert inactivated and diluted
1:10. Sera were also tested for the Waaler-
Rose and the RA-Latex reactions. Fig. 1 gives
the relation between the Waaler-Rose and the
Latex titers, (correllation coefficient r = 0.72)
and the IF-test for IgM-RF. 2 sera with Waaler-
Rose titer 1:20 and RA-Latex titer 1:40 were neg.
by the IF-test for IgM-RF. 3 sera with Waller-
Rose titer 1:10 1:10 and 0 and Latex titer 1:10,
1:20 and 1:40 were positive by the If-test for IgM
RF. Among 20 control sera one was positive for
IgM-RF. The sensitivity of the IF-test seems t--
be as that of the Waaler-Rose and RA-Latex
reactions.
For IgG-RF the sensitivity of the IF-test coulc
assumed to be as for that of IgM-RF or less,
based on the findings that the bindingcoefficients
of 19 S IgM RF, 7S-subunit IgM-RF, and IgG-R I
by reaction with aggregated human IgG are of th:
same magnitude (6).
A possible unspecific reaction in the IF-test t .
IgG-RF could occur if 19 S IgM-RF reacted witl'
serum IgG at some of its bindingsites and binds
to the amboceptor with the others. The serurr
IgG molecules bound to IgM-RF will in the test
system be measured as IgG-RF without having RF
activity. This has been pointed out by Sany (10).
To avoid this serum was treated with dithiothreit'
(DTT) before IF-test for IgG-RF. DTT spHt:
disulphide bands and destroys IgM-antibody
activity without affecting IgG-antibody activify
(2,8). This can be seen in table I, which also
gives the results of the IF-test for IgM-RF anc!
IgG-RF of 54 RA-sera before and after DTT-treat
ment All the sera with pos. IF-test for IgM-RF
before DTT treatment became neg. after the DTT
treatment, just like the RA-Latex test. Among
sera with pos. Waaler-Rose titer > 1:40 29 were
pos. in the IF-test for IgG-RF before and 13 pos.
after DTT treatment. This change is statistically
significant (p< 0.01, X.2-test). Among sera with
a Waaler-Rose titer < 1:40 were 7 pos. in the
IF-test for IgG-RF before DTT treatment and 9
pos. after. Thus it may be seen that positive
reactions for IgG-RF in the IF-test of untreated
sera from patients with Waaler-Rose titer > 1:40
may not only be due to IgG-RF activity, but
probably also that IgM-RF has bound normal