Immunoglobulin gene usage and immunohistochemical characteristics of humanmonoclonal antibodies to the mitochondrial autoantigens of primary biliarycirrhosis induced in the XenoMouse
M. Sasaki et al., Immunoglobulin gene usage and immunohistochemical characteristics of humanmonoclonal antibodies to the mitochondrial autoantigens of primary biliarycirrhosis induced in the XenoMouse, HEPATOLOGY, 34(4), 2001, pp. 631-637
The immunodominant antimitochondrial antibody (AMA) response in primary bil
iary cirrhosis (PBC) is directed against the E2 component of pyruvate dehyd
rogenase (PDC-E2). The nature of the clonal selection process is unclear, a
nd to address this issue, we took advantage of a transgenic technology, Xen
oMouse, that contains 80% of the human immunoglobulin (Ig) variable gene re
pertoire and can produce high-affinity human antibodies to virtually any im
munogen without evidence of clonal bias. We immunized mice with PDC-E2 to o
btain 13 HmAbs, including 4 IgG(2) and 9 IgM isotypes. Immunoglobulin gene
analysis was unique and demonstrated a clonal bias; the immunoglobulin,gene
usage was considerably different from other antibody responses analyzed in
XenoMouse systems. Four of the 13 mAbs recognized the inner lipoyl domain
of PDC-E2, 2 of 13 recognized the entire PDC-E2 molecule, 4 of 13 recognize
d PDC-E2 and OGDC-E2, 1 of 13 recognized OGDC only, 1 recognized BCOADC-E2
only, and I recognized an unidentified 100-kd mitochondrial protein. Immuno
histochemical staining using these HmAbs produced mitochondrial staining of
septal bile ducts in both PBC and control livers. la gene analysis showed
that 7 of 13 HmAbs used the V(H)3 and 4 of 13 used VH4 gene repertoire, res
pectively. Three of 7 V(H)3 antibodies used the same Ig VH3-21 gene family
found in human AMA from patients with PBC. The CDRs of these autoantibodies
were slightly mutated when compared with the sequences present within the
Ig germline genes. In conclusion, the XenoMouse not only recapitulates the
unique specificity and restriction of PBC patients, but indicates that the
autoantibodies are derived from a restricted clonal selection process. Such
data suggest that the original immunogen leads to somatic mutation without
subsequent development of determinant spreading.