Soluble human leukocyte antigen-G serum levels in patients with acquired immune deficiency syndrome affected by different disease-defining conditions before and after antiretroviral treatment

Natural Killer Cell Interactions with Classical and Non-Classical Human Leukocyte Antigen Class I in HIV-1 Infection

Natural killer (NK) cells are effector lymphocytes of the innate immune system that are able to mount a multifaceted antiviral response within hours following infection. This is achieved through an array of cell surface receptors surveilling host cells for alterations in human leukocyte antigen class I (HLA-I) expression and other ligands as signs of viral infection, malignant transformation, and cellular stress. This interaction between HLA-I ligands and NK-cell receptor is not only important for recognition of diseased cells but also mediates tuning of NK-cell-effector functions. HIV-1 alters the expression of HLA-I ligands on infected cells, rendering them susceptible to NK cell-mediated killing. However, over the past years, various HIV-1 evasion strategies have been discovered to target NK-cell-receptor ligands and allow the virus to escape from NK cell-mediated immunity. While studies have been mainly focusing on the role of polymorphic HLA-A, -B, and -C molecules, less is known about how HIV-1 affects the more conserved, non-classical HLA-I molecules HLA-E, -G, and -F. In this review, we will focus on the recent progress in understanding the role of non-classical HLA-I ligands in NK cell-mediated recognition of HIV-1-infected cells.

Immunoregulatory Role of HLA-G in Allergic Diseases

Allergic diseases are sustained by a T-helper 2 polarization leading to interleukin-4 secretion, IgE-dependent inflammation, and mast cell and eosinophil activation. HLA-G molecules, both in membrane-bound and in soluble forms, play a central role in modulation of immune responses. Elevated levels of soluble HLA-G (sHLA-G) molecules are detected in serum of patients with allergic rhinitis to seasonal and perennial allergens and correlate with allergen-specific IgE levels, clinical severity, drug consumption, and response to allergen-specific immunotherapy. sHLA-G molecules are also found in airway epithelium of patients with allergic asthma and high levels of sHLA-G molecules are detectable in plasma and bronchoalveolar lavage of asthmatic patients correlating with allergen-specific IgE levels. Finally, HLA-G molecules are expressed by T cells, monocytes-macrophages, and Langerhans cells infiltrating the dermis of atopic dermatitis patients. Collectively, although at present it is difficult to completely define the role of HLA-G molecules in allergic diseases, it may be suggested that they are expressed and secreted by immune cells during the allergic reaction in an attempt to suppress allergic inflammation.

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 flourescence 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.

Behavior of soluble HLA-A, -B, -C and HLA-G molecules in patients with chronic hepatitis C virus infection undergoing pegylated interferon-α and ribavirin treatment: potential role as markers of response to antiviral therapy

The serum levels of soluble HLA class I antigens (sHLA-A, -B, -C and sHLA-G) were determined in 40 HCV genotype 1-infected patients before (T ₀), after 3, 6, and 12 months (T ₃, T ₆, and T ₁₂) of pegylated-IFN-α plus ribavirin therapy and 6 months (T ₁₈) after the end of treatment. Twenty patients were sustained virological responders (SVR), and 20 were non-responders (NR). sHLA-A, -B, -C levels at T ₀ were significantly higher in both SVR (mean 10.48 μg/ml) and NR (mean 11.87 μg/ml) patients as compared to healthy controls (mean 0.34 μg/ml, p < 0.0001) and HIV-infected subjects (mean 1.22 μg/ml, p < 0.0001). sHLA-G levels at T ₀ were significantly higher in SVR (mean 24.78 ng/ml) and NR (mean 24.93 ng/ml) patients as compared to healthy controls (mean 10.34 ng/ml, p = 0.015 and p = 0.014, respectively) but were lower as compared to HIV-infected subjects (mean 48.00 ng/ml, p < 0.0001). The levels of sHLA-A, -B, -C and sHLA-G significantly decreased in SVR from T ₀ to T ₁₈ (mean 1.64 and 1.43 ng/ml, respectively, p < 0.0001) and correlated with HCV-RNA, AST, ALT, γGT, and ALP levels. The determination of soluble HLA class I levels could be proposed as a surrogate marker to discriminate SVR and NR HCV-infected patients during PEG-IFN-α plus ribavirin therapy.

Immunomodulatory properties of HLA-G in infectious diseases

HLA-G is a nonclassical major histocompatibility complex molecule first described at the maternal-fetal interface, on extravillous cytotrophoblasts. Its expression is restricted to some tissues in normal conditions but increases strongly in pathological conditions. The expression of this molecule has been studied in detail in cancers and is now also beginning to be described in infectious diseases. The relevance of studies on HLA-G expression lies in the well known inhibitory effect of this molecule on all cell types involved in innate and adaptive immunity, favoring escape from immune control. In this review, we summarize the features of HLA-G expression by type of infections (i.e, bacterial, viral, or parasitic) detailing the state of knowledge for each pathogenic agent. The polymorphism, the interference of viral proteins with HLA-G intracellular trafficking, and various cytokines have been described to modulate HLA-G expression during infections. We also discuss the cellular source of HLA-G, according to the type of infection and the potential role of HLA-G. New therapeutic approaches based on synthetic HLA-G-derived proteins or antibodies are emerging in mouse models of cancer or transplantation, and these new therapeutic tools may eventually prove useful for the treatment of infectious diseases.