Suppression of blastogenesis and proliferation of activated CD4+ T cells: intravenous immunoglobulin (IVIg) versus novel anti‐human leucocyte antigen (HLA)‐E monoclonal antibodies mimicking HLA‐I reactivity of IVIg

Activated CD4⁺ T cells undergo blastogenesis and proliferation and they express several surface receptors, including β2‐microglobulin‐free human leucocyte antigen (HLA) heavy chains (open conformers). Intravenous immunoglobulin (IVIg) suppresses activated T cells, but the mechanism is unclear. IVIg reacts with HLA‐Ia/Ib antigens but its reactivity is lost when the anti‐HLA‐E Ab is adsorbed out. Anti‐HLA‐E antibodies may bind to the peptides shared by HLA‐E and the HLA‐I alleles. These shared peptides are cryptic in intact HLA, but exposed in open conformers. The hypothesis that anti‐HLA‐E monoclonal antibodies (mAbs) that mimic HLA‐I reactivity of IVIg may suppress activated T cells by binding to the shared peptides of the open conformers on the T cell surface was tested by examining the relative binding affinity of those mAbs for open conformers coated on regular beads and for intact HLA coated on iBeads, and by comparing the effects on the suppression of phytohaemagglutinin (PHA)‐activated T cells of three entities: IVIg, anti‐HLA‐E mAbs that mimic IVIg [Terasaki Foundation Laboratory (TFL)‐006 and (TFL)‐007]; and anti‐HLA‐E antibodies that do not mimic IVIg (TFL‐033 and TFL‐037). Suppression of blastogenesis and proliferation of those T cells by both IVIg and the anti‐HLA‐E mAbs was dose‐dependent, the dose required with mAbs 50–150‐fold lower than with IVIg. TFL‐006 and TFL‐007 significantly suppressed blastogenesis and proliferation of activated CD4⁺ T cells, but neither the non‐IVIg‐mimicking mAbs nor control antibodies did so. The suppression may be mediated by Fab‐binding of TFL‐006/TFL‐007 to the exposed shared peptides. The mAb binding to the open conformer may signal T cell deactivation because the open conformers have an elongated cytoplasmic tail with phosphorylation sites (tryosine³²⁰/serine³³⁵).     

Immunoglobulin (Ig)G purified from human sera mirrors intravenous Ig human leucocyte antigen (HLA) reactivity and recognizes one's own HLA types,but may be masked by Fab complementarity‐determining region peptide in the native sera

Intravenous immunoglobulin (IVIg) reacted with a wide array of human leucocyte antigen (HLA) alleles, in contrast to normal sera, due possibly to the purification of IgG from the pooled plasma. The reactivity of IgG purified from normal sera was compared with that of native sera to determine whether any serum factors mask the HLA reactivity of anti‐HLA IgG and whether IgG purified from sera can recognize the HLA types of the corresponding donors. The purified IgG, unlike native sera, mirrored IVIg reactivity to a wide array of HLA‐I/‐II alleles, indicating that anti‐HLA IgG may be masked in normal sera – either by peptides derived from soluble HLA or by those from antibodies. A < 3 kDa peptide from the complementarity‐determining region (CDR) of the Fab region of IgG (but not the HLA peptides) masked HLA recognition by the purified IgG. Most importantly, some of the anti‐HLA IgG purified from normal sera – and serum IgG from a few donors – indeed recognized the HLA types of the corresponding donors, confirming the presence of auto‐HLA antibodies. Comparison of HLA types with the profile of HLA antibodies showed auto‐HLA IgG to the donors' HLA antigens in this order of frequency: DPA (80%), DQA (71%), DRB345 (67%), DQB (57%), Cw (50%), DBP (43%), DRB1 (21%), A (14%) and B (7%). The auto‐HLA antibodies, when unmasked in vivo, may perform immunoregulatory functions similar to those of therapeutic preparations of IVIg.     

Serum antibodies to human leucocyte antigen (HLA)‐E,HLA‐F and HLA‐G in patients with systemic lupus erythematosus (SLE) during disease flares: Clinical relevance of HLA‐F autoantibodies

T lymphocyte hyperactivity and progressive inflammation in systemic lupus erythematosus (SLE) patients results in over‐expression of human leucocyte antigen (HLA)‐Ib on the surface of lymphocytes. These are shed into the circulation upon inflammation, and may augment production of antibodies promoting pathogenicity of the disease. The objective was to evaluate the association of HLA‐Ib (HLA‐E, HLA‐F and HLA‐G) antibodies to the disease activity of SLE. The immunoglobulin (Ig)G/IgM reactivity to HLA‐Ib and β2m in the sera of 69 German, 29 Mexican female SLE patients and 17 German female controls was measured by multiplex Luminex^®‐based flow cytometry. The values were expressed as mean florescence intensity (MFI). Only the German SLE cohort was analysed in relation to the clinical disease activity. In the controls, anti‐HLA‐G IgG predominated over other HLA‐Ib antibodies, whereas SLE patients had a preponderance of anti‐HLA‐F IgG over the other HLA‐Ib antibodies. The disease activity index, Systemic Lupus Erythematosus Disease Activity Index (SLEDAI)‐2000, was reflected only in the levels of anti‐HLA‐F IgG. Anti‐HLA‐F IgG with MFI level of 500–1999 was associated with active SLE, whereas inactive SLE revealed higher MFI (>2000). When anti‐HLA‐F IgG were cross‐reactive with other HLA‐Ib alleles, their reactivity was reflected in the levels of anti‐HLA‐E and ‐G IgG. The prevalence of HLA‐F‐monospecific antibodies in SLE patients was also associated with the clinical disease activity. Anti‐HLA‐F IgG is possibly involved in the clearance of HLA‐F shed from lymphocytes and inflamed tissues to lessen the disease's severity, and thus emerges as a beneficial immune biomarker. Therefore, anti‐HLA‐Ib IgG should be considered as a biomarker in standard SLE diagnostics.