Progesterone-induced blocking factor inhibits degranulation of natural killer cells.
OBJECTIVE
During the first trimester of pregnancy, nonclassical (CD3-, CD56+, CD16-, perforin [P]bright+) natural killer (NK) cells comprise the major decidual lymphocyte population. These cells, in spite of their high perforin content, exert a low cytolytic activity. Peripheral blood lymphocytes of healthy pregnant women produce progesterone-induced blocking factor (PIBF), which inhibits NK activity. PIBF-producing cells are likely to be present in decidua and might contribute to low decidual NK activity.


METHODS
Decidual cells obtained from elective pregnancy termination were double labeled for CD56 and PIBF. We tested the effect of PIBF on perforin liberation by activated peripheral blood NK cells.


RESULTS
Sixty percent of decidual lymphocytes were CD56 + and expressed PIBF at the same time. PIBF-treated and untreated peripheral blood NK cells were incubated with K-562 cells, and perforin content of target conjugated NK cells was detected with immunocytochemistry. PIBF treatment of peripheral blood lymphocytes significantly reduced lysis of K-562 cells. Among target bound lymphocytes in PIBF-treated samples, we found a significantly (P < 0.01) higher rate of P+ cells than in untreated samples.


CONCLUSIONS
These data suggest that PIBF inhibits cytotoxicity of NK cells via a block of degranulation, and since decidual NK cells are PIBF+, it cannot be ruled out that this effect of PIBF contributes to low decidual NK activity.
Faust
Z
Z
Department of Microbiology, University Medical School of Pecs, Hungary.
Laskarin
G
G
Rukavina
D
D
Szekeres-Bartho
J
J
D019002:CD56 Antigen / Q000096:biosynthesis; D015550:Cell Degranulation / Q000276:immunology*; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000276:immunology / Q000378:metabolism; D003656:Decidua / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D005260:Female; D006801:Humans; D007694:Killer Cells, Natural / Q000276:immunology* / Q000378:metabolism; D008213:Lymphocyte Activation / Q000276:immunology; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D054353:Perforin; D052899:Pore Forming Cytotoxic Proteins; D011247:Pregnancy; D011257:Pregnancy Proteins / Q000096:biosynthesis / Q000502:physiology*; D013491:Suppressor Factors, Immunologic / Q000494:pharmacology*
D019002:CD56 Antigen; D008562:Membrane Glycoproteins; C110058:PIBF1 protein, human; D052899:Pore Forming Cytotoxic Proteins; D011257:Pregnancy Proteins; D013491:Suppressor Factors, Immunologic; D054353:Perforin