Significance of fatty acids in pregnancy-induced immunosuppression

Abstract

Pregnancy can exert suppressive effects on chronic inflammatory conditions. We have previously demonstrated a depression in polymorphonuclear leukocyte (PMN) respiratory burst during pregnancy which could explain this amelioration. To elucidate the biochemical mechanism, we have examined PMN phospholipase A2 (PLA2) activity and its relationship to cellular and circulating fatty acids in pregnant women (30 to 34 weeks) and nonpregnant controls. PMN PLA2 activity was determined by arachidonic acid (AA) and leukotriene B4 (LTB4) release, respiratory burst activity was determined by lucigenin-enhanced chemiluminescence, and total serum and PMN fatty acid levels were determined by gas-liquid chromatography. AA release was significantly reduced for pregnancy PMNs in response to N-formyl-met-leu-phe (fMLP) under unprimed and tumor necrosis factor alpha (TNF-alpha)- or interleukin 8-primed conditions. Similarly, LTB4 liberation was significantly reduced in response to fMLP and phorbol myristate acetate in unprimed and TNF-alpha-primed pregnancy PMNs. All major fatty acid classes were altered in the pregnant state. Of these differences in PMNs, oleic acid and alpha-linolenic acid showed a significant increase (13 and 26%, respectively) and stearic acid and AA showed a significant decrease (8 and 30%, respectively). The stearic acid, oleic acid, and AA compositions of all cells analyzed correlated with their corresponding changes in serum fatty acid levels. Crossover serum incubations modified both fatty acid profiles and the PMN respiratory burst accordingly, while individual fatty acid incorporation studies highlighted the importance of polyunsaturated fatty acids for NADPH oxidase efficiency. These findings indicate that the attenuation of PMN function in pregnancy may originate from a reduction in the available pool of cellular fatty acids. Furthermore, this reduction arises as a direct result of a pregnancy-induced shift in circulating fatty acids from polyunsaturated to monounsaturated forms.

FIG. 1

Comparison of AA liberation from PMN of women in their third trimester of pregnancy (n = 6) and nonpregnant age-matched women (n = 6). The results represent the extracellular release of [³H]AA from radioisotope-loaded, fMLP-stimulated PMN under primed (TNF-α, IL-1β, IL-8, and cytochalasin B [cyto b]) and unprimed conditions. The data are expressed as mean ± SEM and are significantly different (P values) at the following levels: ∗, <0.05; ∗∗, <0.02. Significance was determined with the Mann-Whitney U test.

FIG. 2

Comparison of LTB₄ release by PMN of pregnant women (30 to 34 weeks of gestation) and nonpregnant women following fMLP and PMA activation under TNF-α-primed and unprimed conditions. The data are expressed as mean ± SEM and are significantly different at a P value of <0.05 (Mann-Whitney U test) (asterisks).

FIG. 3

Ratios of mean fatty acids in PMN and serum for pregnant women (30 to 34 weeks of gestation) and nonpregnant women. SFA, saturated fatty acids. The degree of statistical significance is indicated by asterisks (P, <0.05) (Mann-Whitney U test).

FIG. 4

Linear regression plot of AA content and fMLP-stimulated superoxide anion release for PMN of pregnant women (30 to 34 weeks of gestation) and nonpregnant age-matched women. The relationship between parameters was significant at a P value of <0.05 (r, Spearman’s rho correlation coefficient). RLU, relative light units.

FIG. 5

Incubation of PMN in environments enriched for saturated fatty acids (FA), MUFA, and PUFA. Isolated PMN were incubated for 5 h at 37°C in a 1:1 molar ratio of individual fatty acids complexed with BSA. The final concentrations of fatty acids was 33 μM, and control samples were incubated in BSA alone. Cellular fatty acid profiles and chemiluminescence responses to fMLP were recorded for the washed cells. The data are expressed as mean ± SEM for six different PMN donors. The results were significantly different (P values) at the following levels: ∗, <0.05; ∗∗, <0.01. Significance was determined with the Wilcoxon rank sum test.

FIG. 6

Serum incubation study for nonpregnancy PMN. The effect of pregnancy serum (50% [vol/vol]) on the fatty acid content and fMLP-stimulated superoxide anion release of normal nonpregnancy PMN was examined. Isolated peripheral blood PMN from nonpregnant subjects were incubated (5 h, 37°C) in either heat-inactivated (56°C, 30 min) autologous serum or heat-inactivated pooled pregnancy sera (n = 6). The data are expressed as mean ± SEM for eight different PMN donors. The results were significantly different (P values) at the following levels: ∗, <0.05; ∗∗, <0.01. Significance was determined with the Wilcoxon rank sum test. RLU, relative light units.

FIG. 7

Serum incubation study for pregnancy PMN. The effect of nonpregnancy serum (50% [vol/vol]) on the fatty acid content and fMLP-stimulated superoxide anion release of pregnancy PMN was examined. Isolated peripheral blood PMN from pregnant subjects were incubated (5 h, 37°C) in either heat-inactivated (56°C, 30 min) autologous serum or heat-inactivated pooled nonpregnancy sera (n = 6). The data are expressed as mean ± SEM for seven different PMN donors. The results were significantly different (P values) at the following levels: ∗, <0.05; ∗∗, <0.03. Significance was determined with the Wilcoxon rank sum test. RLU, relative light units.