We have identified and characterised three new idiotypes on human IgM
McAbs generated from the splenocytes of a SLE patient with active dise
ase. RT-6, which binds H1 and Sm/RNP, expresses essentially a private
Id. Its expression is limited to a small number of human McAbs and the
sera from patients with infectious diseases. In contrast RT-72Id and
RT-84Id, expressed on McAbs which are polyreactive for two or more ant
igens, have a public distribution. RT-72Id and RT-84Id are found on Mc
Abs from murine and human adult, and foetal tissues. In sera, signific
ant numbers of SLE, RA and patients with other autoimmune diseases are
positive for both Ids. RT-84Id is also elevated in SLE relatives and
spouses, and in patients with Klebsiella infection. No correlation wit
h disease activity, IgM or IgG levels was observed with either Id. How
ever, RT-72Id was significantly associated with anti-ssDNA antibodies
and RhF RT-6Id and RT-72Id are located on the framework regions of the
mu heavy chain, whereas RT-84Id is present on the kappa light chain,
within the binding site. The McAbs are encoded by mainly germline gene
s: heavy chains of RT-6, RT-72 and RT-84 are encoded by the genes VH26
, VH4.22 and VH4.21, respectively, and the light chain sequences of RT
-6 and RT-72 are derived from DPL11 and HK102. Immunofluorescent stain
ing revealed the presence of RT-72Id and RT-84Id positive immunoglobul
in deposits in 18% and 45%, respectively, of the lupus renal sections
compared with none in the disease control group, suggesting that these
Ids may contribute to the pathology of the disease.