Anti-citrullinated-protein-antibody-specific intravenous immunoglobulin attenuates collagen-induced arthritis in mice.

Administration of intravenous immunoglobulin (IVIg) is a recognized safe and efficient immunomodulation therapy for many autoimmune diseases. Anti-idiotypic antibody binding to pathogenic autoantibodies was proposed as one of the mechanisms attributed to the protective activity of IVIg in autoimmunity. The aim of this study was to fractionate the anti-anti-citrullinated protein anti-idiotypic-antibodies (anti-ACPA) from an IVIg preparation and to test it as a treatment for collagen-induced arthritis in mice. IVIg was loaded onto an ACPA column. The eluted fraction was defined as ACPA-specific-IVIg (ACPA-sIVIg). Collagen-induced-arthritis (CIA) was induced in mice. Mice were treated weekly with ACPA-sIVIg, low-dose-IVIg, high-dose-IVIg and phosphate-buffered saline (PBS). Sera-ACPA titres, anti-collagen anitbodies and cytokine levels were analysed by enzyme-linked immunosorbent assay (ELISA); antibody-forming-cell activity by enzyme-linked imunospot (ELISPOT) assay; and expansion of regulatory T cell (Treg ) population by fluorescence activated cell sorter (FACS). ACPA-sIVIg inhibited ACPA binding to citrullinated-peptides (CCP) in vitro 100 times more efficiently than the IVIg compound. ACPA-sIVIg was significantly more effective than the IVIg-preparation in attenuating the development of collagen-induced arthritis. Splenocytes from CIA mice treated with ACPA-sIVIg reduced the ACPA and anti-collagen-antibody titres, including the number of anti-collagen and ACPA antibody-forming cells. In parallel, splenocytes from ACPA-sIVIg treated mice secreted higher levels of anti-inflammatory cytokines and lower proinflammatory cytokines. The ACPA-sIVIg inhibitory potential was accompanied with expansion of the Treg population. Low-dose IVIg did not affect the humoral and cellular response in the CIA mice in comparison to the PBS-treated mice. Based on our results, IVIg may be considered as a safe compound for treating patients with rheumatoid arthritis by neutralizing pathogenic autoantibodies, reducing proinflammatory cytokines and expanding the Treg population.

HLA-G levels in serum and plasma.

Soluble human leukocyte antigen (HLA)-G levels are in most cases higher in the plasma than in the serum obtained from the same individual. This is probably due to trapping of the protein during clot formation. In studies where soluble HLA-G is quantified, it is therefore recommended that plasma or serum levels should be compared with the same blood product, namely, serum to serum and plasma to plasma. Because of possible gender differences in HLA-G levels it is also recommended that this should be considered in the construction of a control group especially in studies where there is a preponderance of one of the sexes.

HLA-G levels in serum and plasma.

HLA-G belongs to the non-classical HLA class-I family of genes presently designated as class-Ib genes. There are four membrane-bound (HLA-G1 to -G4) and three soluble forms (HLA-G5 to -G7) generated by alternative splicing of the primary transcript. HLA-G in the soluble form is found in the plasma, amniotic fluid, and cord blood of healthy individuals. Quantitative determination suggested that HLA-G levels are genetically controlled. While quantifying soluble HLA-G by ELISA, we observed that when plasma and serum levels were measured for the same individual, HLA-G plasma values were almost invariably higher than those from serum. Our results suggest that HLA-G is trapped and/or consumed during clot formation. The amount trapped within the clot is variable and inconsistent. To obtain values which reflect the true biological levels, it is therefore recommended that HLA-G should be determined in the plasma. If serum levels are determined, they should be compared with matched control sera. It should always be borne in mind that conclusions concerning sera levels might be erroneous, because the true plasma level of the protein can be significantly higher.