Background/Purpose: Pentraxin 3
(PTX3) is an acute-phase protein released by different cell types including renal
epithelial cells and immune-competent cells. PTX3 is able to either dampen or
fuel inflammation through binding of apoptotic cells and complement fragment 1
(C1q).

Anti-dsDNA
and anti-C1q antibodies are associated with lupus glomerulonephritis (LGN). By
contrast, we have recently demonstrated a negative association between anti-PTX3
antibodies and LGN and a direct correlation between PTX3 renal staining and
proteinuria in SLE patients.

Hereby
we aim at exploring effects of anti-PTX3 antibodies in a murine model of SLE, focusing
on lupus-like nephritis.

Methods: Thirty New
Zealand Black/White (NZB/NZW F1) mice were split into 3 groups of 10 mice each
and intraperitoneally injected with 100 µg of PTX3 in 100 µl of alum and 100 µl
of phosphate buffer saline (PBS) (group 1), 100 µl of alum and 100 µl of PBS
(group 2) or 200 µl of PBS (group 3), 3 times 3 weeks apart from the 11^th
week of age, until natural death.

We
analyzed titers and time of occurrence of anti-PTX3, anti-dsDNA and anti-C1q
antibodies by monthly blood sampling since week 11. Antibody serum levels were evaluated
by standardized home-made ELISA and expressed as the median (min-max) of the
mean optical density of the double of every serum.

Proteinuria
was weekly examined by multireactive strips (Siemens). Survival and
proteinuria-free survival (<300 mg/dl) were evaluated according to
Kaplan-Meier method.

Kidneys,
lungs, liver and spleen were harvested at death for histological analysis. Expression
of collagen (Coll)-IV and TGF-β mRNA was evaluated on kidney specimens by
spectrophotometric analysis.

IBM
SPSS Statistics 22 for Windows software (IBM SPSS Inc., USA) was used for
statistical analysis.

The
study was approved by the National Institutional Animal Care and Use Committee.

Results: Serum autoantibody
and proteinuria levels are reported in Table 1. Only group 1 mice developed
anti-PTX3 antibodies. Anti-dsDNA and anti-C1q antibodies appeared significantly
later and at lower titer in group 1 vs. group 2 and 3 (p<0.0001). Group 1
mice lived significantly longer than control mice (p=0.03) and had proteinuria
significantly delayed and reduced (p<0.05, weeks 22 to 28).

Coll-IV
and TGF-β mRNA were found less frequently in kidneys from group 1 mice vs.
group 2 and 3 (TGF-β, group 1 vs. group 2, p =0.028; group 1 vs. group 3
p=0.042; Coll-IV group 1 vs. group 2, p=0.018; group 1 vs. group 3, p= 0.029). No
significant difference was found in group 2 vs. group 3.

Harvested
organs displayed inflammatory lesions in all mice, albeit milder lesions in
group 1. Seven out of 10 mice of group 2 and all mice of group 3 had mesangial
hyperplasia and renal perivascular lymphoplasmocitosis, not found in group 1.

Conclusion: Anti-PTX3
antibodies seem to attenuate and delay lupus-like manifestations including LGN
in NZB/NZW F1 mice