Parasites break down mucous barrier in intestines to infect host

This is the first time it has been elucidated how the pathogenic organism goes about penetrating a protective mucous layer. The findings are presented in the latest issue of the prestigious scientific journal Proceedings of the National Academy of Sciences in the U.S.

The parasite Entamoeba histolytica is extremely common, but many people live with the amoeba in their body without noticing it. Some 500 million people around the world carry the parasite, but only one tenth of them develop symptoms.

The amoeba can infect the large intestine and cause bloody diarrhea. If the parasite penetrates further into the body, it can form cysts in the liver, and the disease can be fatal.

The stomach and intestines are protected by a layer of mucous that is extra thick and dense in the large intestine. This mucous is made up of large carbohydrate-rich protein molecules called mucins. The mucous layer forms a barrier that is difficult to penetrate and normally cannot be broken down, but organisms that cause disease in the large intestine nevertheless managed to get through.

The article shows that the amoeba Entamoeba histolytica secrets specific protein-cleaving enzymes that can split the mucin, causing the network to collapse.

“The amoeba enzyme cleaves the mucin at a very particular and unusual protein sequence. This allows the amoeba to bore through the mucous layer like a projectile and infect the underlying epithelial cells of the intestine,” says research Martin Lidell.

In the Third World nearly 100,000 people die each year as a result of complications following amoeba infections.

“We now have a better understanding of amoeba infections, and this knowledge provides us with the possibility of designing drugs that can prevent the amoeba from breaking down the mucous barrier and thereby infect the person,” says Professor Gunnar C. Hansson, who directs mucin biological research at the Sahlgrenska Academy.

This research is being carried out in collaboration with amoeba experts in Canada.

Journal: Proceedings of the National Academy of Sciences, U.S.

Title of article: Entamoeba histolytica cysteine proteases cleave the MUC2 mucin in its C-terminal domain and dissolve the protective colonic mucus gel

Authors: Martin E. Lidell, Darcy M. Moncada, Kris Chadee, and Gunnar C. Hansson