Altered circulating levels of matrix metalloproteinases and inhibitors associated with elevated type 2 cytokines in lymphatic filarial disease

Abstract

Background: Infection with Wuchereria bancrofti can cause severe disease characterized by subcutaneous fibrosis and extracellular matrix remodeling. Matrix metalloproteinases (MMPs) are a family of enzymes governing extracellular remodeling by regulating cellular homeostasis, inflammation, and tissue reorganization, while tissue-inhibitors of metalloproteinases (TIMPs) are endogenous regulators of MMPs. Homeostatic as well as inflammation-induced balance between MMPs and TIMPs is considered critical in mediating tissue pathology.

Methods: To elucidate the role of MMPs and TIMPs in filarial pathology, we compared the plasma levels of a panel of MMPs, TIMPs, other pro-fibrotic factors, and cytokines in individuals with chronic filarial pathology with (CP Ag+) or without (CP Ag-) active infection to those with clinically asymptomatic infections (INF) and in those without infection (endemic normal [EN]). Markers of pathogenesis were delineated based on comparisons between the two actively infected groups (CP Ag+ compared to INF) and those without active infection (CP Ag- compared to EN).

Results and conclusion: Our data reveal that an increase in circulating levels of MMPs and TIMPs is characteristic of the filarial disease process per se and not of active infection; however, filarial disease with active infection is specifically associated with increased ratios of MMP1/TIMP4 and MMP8/TIMP4 as well as with pro-fibrotic cytokines (IL-5, IL-13 and TGF-β). Our data therefore suggest that while filarial lymphatic disease is characterized by a non-specific increase in plasma MMPs and TIMPs, the balance between MMPs and TIMPs is an important factor in regulating tissue pathology during active infection.

Figure 1. Filarial lymphedema is associated with elevated levels of MMPs.

(A) Plasma levels of MMP-1, -7, -8, and -9 from filarial lymphedema individuals with active infection [CP Ag+] (n = 28) and asymptomatic infected [INF] (n = 74) individuals were measured by ELISA. (B) Plasma levels of MMP-1, -7, -8 and -9 from filarial lymphedema individuals without active infection [CP Ag−] (n = 77) and endemic normal [EN] (n = 73) individuals were measured by ELISA. P values were calculated using the Mann-Whitney test.

Figure 2. Filarial lymphedema is associated with elevated levels of TIMP-1 and 2.

(A) Plasma levels of TIMP-1, -2, -3, and -4 from filarial lymphedema individuals with active infection [CP Ag+] (n = 28) and asymptomatic infected [INF] (n = 66–76) individuals were measured by ELISA. (B) Plasma levels of TIMP-1, -2, -3, and -4 from filarial lymphedema individuals without active infection [CP Ag−] (n = 66–76) and endemic normal [EN] (n = 73) individuals were measured by ELISA. P values were calculated using the Mann-Whitney test.

Figure 3. Altered MMP to TIMP ratios in filarial infection and lymphedema.

(A) Ratio of circulating levels of MMP-1/TIMP-4 and MMP-8/TIMP-4 from filarial lymphedema individuals with active infection [CP Ag+] and asymptomatic infected [INF] individuals as well as from filarial lymphedema individuals without active infection [CP Ag−] and endemic normal [EN] individuals are shown. (B) Ratio of circulating levels of MMP-1/TIMP-2, MMP-7/TIMP-1, and MMP-7/TIMP-2 from filarial lymphedema individuals with active infection [CP Ag+] and asymptomatic infected [INF] individuals as well as from filarial lymphedema individuals without active infection [CP Ag−] and endemic normal [EN] individuals are shown. P values were calculated using the Mann-Whitney test.

Figure 4. Filarial lymphedema is not associated with elevated levels of FGF-2 or PDGF-AA.

(A) Plasma levels of FGF-2 and PDGF-AA from filarial lymphedema individuals with active infection [CP Ag+] (n = 21–22) and asymptomatic infected [INF] (n = 22–39) individuals were measured by ELISA. (B) Plasma levels of FGF-2 and PDGF-AA from filarial lymphedema individuals without active infection [CP Ag−] (n = 22–38) and endemic normal [EN] (n = 21–33) individuals were measured by ELISA. P values were calculated using the Mann-Whitney test.

Figure 5. Circulating levels of pro-fibrotic cytokines in filarial lymphedema.

(A) Plasma levels of IL-5, IL-13, and TGF-β from filarial lymphedema individuals with active infection [CP Ag+] (n = 24) and asymptomatic infected [INF] (n = 90) individuals were measured by ELISA. (B) Plasma levels of IL-5, IL-13, and TGF-β from filarial lymphedema individuals without active infection [CP Ag−] (n = 70–91) and endemic normal [EN] (n = 68–80) individuals were measured by ELISA. P values were calculated using the Mann-Whitney test.

Figure 6. Correlation between MMP/TIMP ratios and Type 2 cytokines in filaria-infected individuals.

(A) MMP/TIMP ratios were correlated with the levels of IL-13 from individuals with active infection [CP Ag+ and INF (n = 102–114)]. (B) MMP/TIMP ratios were correlated with the levels of IL-5 from individuals with active infection [CP Ag+ and INF (n = 102–114)]. CP Ag+ individuals are shown in gray circles and INF in dark circles. P and r values were calculated using the Spearman rank correlation test.