The secreted triose phosphate isomerase of Brugia malayi is required to sustain microfilaria production in vivo

Human lymphatic filariasis is a major tropical disease transmitted through mosquito vectors which take up microfilarial larvae from the blood of infected subjects. Microfilariae are produced by long-lived adult parasites, which also release a suite of excretory-secretory products that have recently been subject to in-depth proteomic analysis. Surprisingly, the most abundant secreted protein of adult Brugia malayi is triose phosphate isomerase (TPI), a glycolytic enzyme usually associated with the cytosol. We now show that while TPI is a prominent target of the antibody response to infection, there is little antibody-mediated inhibition of catalytic activity by polyclonal sera. We generated a panel of twenty-three anti-TPI monoclonal antibodies and found only two were able to block TPI enzymatic activity. Immunisation of jirds with B. malayi TPI, or mice with the homologous protein from the rodent filaria Litomosoides sigmodontis, failed to induce neutralising antibodies or protective immunity. In contrast, passive transfer of neutralising monoclonal antibody to mice prior to implantation with adult B. malayi resulted in 60–70% reductions in microfilarial levels in vivo and both oocyte and microfilarial production by individual adult females. The loss of fecundity was accompanied by reduced IFNγ expression by CD4+ T cells and a higher proportion of macrophages at the site of infection. Thus, enzymatically active TPI plays an important role in the transmission cycle of B. malayi filarial parasites and is identified as a potential target for immunological and pharmacological intervention against filarial infections

Natriuretic peptides and their receptors in human neural retina and retinal pigment epithelium

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) play a role in transepithelial fluid movement in the kidney and at the blood-aqueous barrier. We sought a similar natriuretic peptide-mediated regulatory system at the level of the blood-retinal barrier by investigating human neural retina and retinal pigment epithelium for the presence of ANP, BNP and their receptors. ANP and BNP binding to receptors could be demonstrated autoradiographically in all layers of the retina inclusive of the retinal pigment epithelium. Competitive preincubation with unlabeled peptides blocked the binding of the respective radioactive peptide. ANP and BNP could also be demonstrated immunohistochemically in both the neural retina and the retinal pigment epithelium. Our results suggest a role of these peptides both in the regulation of intraretinal fluid movement and--by analogy with other peptides--as possible neutrotransmittors. The localisation of ANP and BNP in the retinal pigment epithelium suggests that these peptides may influence ocular fluid homeostasis at the outer blood-retinal barrier by modulating pigment epithelial function

Insulin-like growth factor I (IGF-I) receptor/binding protein in human diabetic epiretinal membranes

Insulin-like growth factor I (IGF-I) is thought to play a role in the development of proliferative diabetic retinopathy. Proliferative diabetic retinopathy is characterised by the formation of fibrovascular epiretinal membranes, and IGF-I may initiate and/or potentiate this epiretinal proliferation. To evaluate further the part played by IGF-I in the development of epiretinal tissue, we investigated the presence of IGF-I receptor/binding protein in proliferating diabetic fibrovascular epiretinal membranes. Five fibrovascular epiretinal membranes were obtained by vitrectomy from five patients with proliferating diabetic retinopathy. The presence of IGF-I receptors was investigated by autoradiography using 125I-labeled IGF-I on frozen sections. To characterise binding specificity, some sections were preincubated with either insulin or unlabeled IGF-I. Sections of post-mortem liver were used as controls. Strong labeling of cells with 125I-labeled IGF-I was observed in all epiretinal membranes and in liver cells. Almost no autoradiographic labeling was observed in sections that had been blocked with non-radioactive IGF-I, and very little labeling was found following blockage with insulin. Our preliminary study suggests the presence of IGF-I receptor/binding protein in human diabetic epiretinal membranes. These results support the hypothesis that IGF-I may be involved in the formation of proliferative diabetic membranes