Table 3.
Summary of the studies that reported the association of HLA-G polymorphisms with sHLA-G expression in patients attending IVF treatment.
| Study | Country | Ethnicity | Study population | Number of patients tested | Sample tested | Timing of sample collection | Type of assay | sHLA-G isoform | Detection limit | Result | Included in meta-analysis |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Papúchová 2022 (41) | Denmark | Caucasian | Women attending IVF treatment | 121 | Endometrium | the day equivalent to embryo transfer | IH | HLA-G5 and HLA-G6 | NR | No significant differences were observed in sHLA-G expression between the different HLA-G genotypes | No |
| Piekarska 2021 (76) | Poland | Caucasian | Men attending IVF treatment | 183 | Seminal plasma | 2-7 days of sexual abstinence | ELISA | HLA-G1 and HLA-G5 | 0.6 IU/ml | Certain HLA-G haplotypes and diplotypes of rs1632947-rs1233334-rs371194629 are associated with seminal sHLA-G expression | No |
| Nilsson 2020 (79) | Denmark | Caucasian | Couples attending IVF treatment | 127 couples and 4 single women | Periphery blood plasma and seminal plasma | NR | ELISA | HLA-G1 and HLA-G5 | 0.6 IU/ml | HLA-G 14bp genotype or HLA-G 3’UTR diplotype is significantly associated with seminal sHLA-G levels, while is not significantly associated with female blood plasma sHLA-G levels | Yes |
| Nowak 2020 (8) | Poland | Caucasian | Women attending IVF | 234 before IVF-ET and 185 after IVF-ET | Periphery blood plasma | Before and after IVF-ET | ELISA | HLA-G1 and HLA-G5 | 0.6 IU/ml | Certain HLA-G haplotypes of rs1632947-rs1233334-rs371194629 are associated with sHLA-G expression in blood plasma before IVF-ET; whereas such observations were not detected after ET | No |
| Craenmehr 2019 (77) | Netherlands | Caucasian | Men attending IVF treatment | 156 | Seminal plasma | NR | ELISA | HLA-G1 and HLA-G5 | 0.6 IU/ml | Seminal plasma sHLA-G levels are associated with HLA-G SNPs (HLA-G 14 bp ins/del, +3003 C/T, +3010 C/G, +3142 C/G, +3187 A/G, +3196 C/G, +3496 A/G and + 3509 G/T) and haplotypes at the 3’UTR | Yes |
| Nardi 2016 (35) | Brazil | Mixed | RIF and control patients | 58 | Periphery blood serum | NR | ELISA | HLA-G1 and HLA-G5 | 0.25ng/ml | HLA-G 14bp del variant is associated with higher sHLA-G levels | Yes |
| Dahl 2014 (78) | Denmark | Caucasian | Couples attending IVF treatment | 43 men for seminal test; 53 women and 47 men for blood test | Seminal plasma and periphery blood plasma | NR | ELISA | HLA-G1 and HLA-G5 | 0.6 IU/ml | Male HLA-G 14bp del/del genotype is associated with higher sHLA-G levels in seminal plasma | Yes |
| Nardi 2012 (19) | Brazil | Mixed | RIF and control patients | 41 RIF women and 60 controls | Periphery blood serum | NR | ELISA | HLA-G1 and HLA-G5 | 3.9U/ml | HLA-G allele distribution in exon 2,3,4 is not associated with serum sHLA-G levels | No |
| Sipak-Szmigiel 2007 (70) | Poland | Caucasian | Women attending IVF treatment | 80 | Periphery blood plasma | NR | ELISA | NR | 2U/ml | Allele HLA-G10101, 10102, and 10108 was related to higher plasma sHLA-G levels than other alleles | No |
| Hviid 2004 (75) | Denmark | Caucasian | Couples attending IVF treatment | 43 women and 42 male partners | Periphery blood serum | Before pregnancy | ELISA | HLA-G1 and HLA-G5 | 1ng/ml | Detectable sHLA-G in serum is restricted to HLA-G genotypes with the 14bp del | No |
IH, Immunohistochemical staining; ELISA, enzyme-linked immunosorbent assay; IVF, in vitro fertilization; ET, embryo transfer; 3’UTR, 3’ untranslated region; 5’ URR, 5’ upstream regulatory region; NR, not reported.