Helminth species specific expansion and increased TNF-alpha production of non-classical monocytes during active tuberculosis

• Author summary Monocytes are important cells for the early innate immune response and play an integral part during inflammation and infection. Classical monocytes, the dominant monocyte subset during homeostasis and health, have been linked to efficient TB protection. Intermediate or non-classical monocytes have instead been associated with uncontrolled inflammation (TNF-alpha), cell death, and poor protection against Mycobacterium tuberculosis. In areas endemic for intestinal helminths, the immunoregulatory effects of monocytes may affect development or progression of TB disease. The role of monocyte subsets during helminth/TB coinfection have not been studied. In Gondar, Ethiopia, we show that in patients with helminth infection, a helminth species dependent expansion of non-classical monocytes is triggered, where Ascaris and hookworm had the strongest effect in coinfected pulmonary TB-patients. The increase in non-classical monocytes was mainly detected in coinfected patients with a low-to-intermediate disease severity. Only coinfection with helminths and TB induced an increased TNF-alpha response in monocytes. Thus, we found a helminth species-specific dysregulation of monocyte subset distribution and functionality in coinfected TB-patients which could affect TB pathogenesis. Both Mycobacterium tuberculosis infection and helminths may affect innate immune mechanisms such as differential effects on monocytes towards the non-classical and intermediate subsets that favor bacterial persistence. Our aim, was to investigate helminth species specific effects on the frequency and functional activity of monocyte subsets in patients with active tuberculosis and healthy subjects. HIV-negative patients with active pulmonary tuberculosis (PTB) and community controls (CCs) in Gondar, Ethiopia were screened for helminth infection by stool microscopy. Flow cytometric analysis of peripheral blood mononuclear cells (PBMCs) and ex vivo stimulation with purified protein derivative (PPD) and helminth antigens were used to characterize the distribution of monocyte subsets and their function. A total of 74 PTB patients and 57 CCs with and without helminth infection were included. Non-classical monocytes were increased in PTB patients with Ascaris and hookworm infection but not in Schistosoma-infected patients. Ascaris had the strongest effect in increasing the frequency of non-classical monocytes in both PTB patients and CCs, whereas PTB without helminth infection did not affect the frequency of monocyte subsets. There was a helminth specific increase in the frequency of TNF-alpha producing non-classical monocytes in hookworm infected PTB patients, both with and without PPD-stimulation. Low-to-intermediate TB disease severity associated with increased frequency of non-classical monocytes only for helminth-positive PTB patients, and the frequency of TNF-alpha producing monocytes were significantly higher in intermediate and non-classical monocytes of helminth positive PTB patients with an intermediate disease score. Helminth infection affected the frequency of monocyte subsets and function both in TB patients and controls which was helminth species dependent in TB patients. The clinical role of this potential immunomodulatory effect needs further study and may affect the response and protection to tuberculosis in areas where helminth infections are endemic.

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MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Infektionsmedicin (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Infectious Medicine (hsv//eng)

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