Reduced Mycobacterium tuberculosis association with monocytes from diabetes patients that have poor glucose control

Abstract

The re-emerging importance of type 2 diabetes mellitus (DM) to tuberculosis (TB) control is of growing concern, but the basis for this relationship is poorly understood. Given the importance of mononuclear phagocytes for TB control and the reported alterations in monocytes of DM patients, we evaluated whether the initial interaction between both was affected in diabetics. Mycobacterium tuberculosis-naïve individuals with and without DM were group matched by age and gender and the efficiency of M. tuberculosis association (attachment and ingestion) with their monocytes was assessed in the presence of autologous serum. The association of M. tuberculosis with monocytes was significantly lower in diabetics (19.2 ± 6.1) than non-diabetics (27.5 ± 7.9; p = 0.02). Multivariate analysis controlling for host socio demographics, DM characteristics and serum lipids indicated that male gender (p = 0.04) and poorly-controlled DM (high HbA1c and hyperglycemia; p = 0.01) were significantly associated with the lower interaction of M. tuberculosis with monocytes. Serum heat-inactivation reduced the association of M. tuberculosis to similar levels in both study groups (p = 0.69) suggesting alterations in the complement pathway of DM patients. These findings suggest an altered route of entry of the pathogen in DM patients that may influence the downstream activation of signaling pathways in the monocyte and the survival of mycobacteria.

Figure 1. M. tuberculosis association with monocytes from participants with or without DM

M. tuberculosis-GFP was incubated with the monocytes from eight participants without DM and nine with DM, either borderline (n=4) or poorly-controlled DM (n=5). After 2h the monocytes with associated mycobacteria were fixed and monocyte nuclei stained with DAPI. The percentage of monocytes with at least one associated M. tuberculosis (green) was calculated by counting at least 200 cells (blue) using fluorescence microscopy. A. Representative high power field (63×) showing three monocytes with associated M. tuberculosis (arrows) and one with no M. tuberculosis (arrowhead) B. The mean and standard deviation (error bars) are shown for M. tuberculosis association with monocytes from no DM (open bar) and DM (gray bar) under culture conditions with 5% or 20% autologous serum. Differences between no DM and DM were assessed by the student’s t-test.