Blastocystosis - Pathogeneses

Pathogeneses

Pathogenesis refers to the mechanism by which an organism causes disease. The following disease-causing mechanisms have been reported in studies of Blastocystis infection:

• Barrier Disruption: In isolates from Blastocystis sp. subtype 4, study has demonstrated that Blastocystis has the ability to alter the arrangement of F-actin in intestinal epithelial cells. Actin filaments are important in stabilizing tight junctions; they in turn stabilize the barrier, which is a layer of cells, between the intestinal epithelial cells and the intestinal content. The parasite causes the actin filaments to rearrange, and so compromising barrier function. This has been suggested to contribute to the diarrheal symptoms sometimes observed in Blastocystis patients.

• Invasiveness: Invasive infection has been reported in humans and animal studies.

• Immune Modulation: Blastocystis has been shown to provoke cells from the human colon to produce inflammatory cytokines Interleukin-8 and GM-CSF. Interleukin-8 plays a role in rheumatoid arthritis.

• Protease Secretion: Blastocystis secretes a protease that breaks up antibodies produced and secreted into the gastrointestinal tract lumen. These antibodies, known as immunoglobulin A (IgA), make up the immune defense system of human by preventing the growth of harmful microorganisms in the body and by neutralizing toxins secreted by these microorganisms. By breaking up the antibodies, it allows the persistence of Blastocystis in the human gut. Another more recent study has also shown and proposed that, in response to the proteases secreted by Blastocystis, the intestinal host cells would signal a series of events to be carried out, eventually leading to the self-destruction of the host cells – a phenomenon known as apoptosis

• Other secretory mechanism: A study of a different protozoan which produces similar symptoms, Entamoeba histolytica, found that organism secretes several neurologically active chemicals, such as serotonin and Substance P. Serum levels of serotonin have been found to be elevated in patients with Entamoeba histolytica. One paper noted the diffuse symptoms of Blastocystis infection correlate with serotonin's role in the body, and suggested a similar mechanism may be present in Blastocystis infection.