An increased incidence of diseases of immune dysregulation in developed communities over the past 4 decades has led to a search for the environmental factors driving these changes. Published evidence points towards a relative lack of environmental or intestinal exposure to the gram-negative bacterial product, lipopolysaccharide (LPS) as a possible molecular explanation of those epidemiological observations.
Hypothesis:
Reduced long term exposure to inhaled LPS and / or reduced intestinal gram-negative bacterial exposure down-regulates expression of the immunomodulatory factors FoxP3 and CD101.
Flow cytometry was used to quantify the effects of long-term, inhaled LPS and separately the presence or absence of enteric gram-negative bacteria on expression of CD101, FoxP3 and IL-17a in splenocytes.
Cohorts of pregnant Balb/C dams received either no additional LPS - mimicking hygienic living; low dose inhaled LPS mimicking aggricultural environments or high dose LPS aimed at sub-clinical toxicity. The LPS was aerosolised daily into closed cages. Sub-cohorts of each LPS inhalation regimen received either (a) sterile water or (b) Cefoxitin and Gentamicin in their drinking water.
All mice were sacrificed when the pups were 5 weeks old. Spleens were processed into single cell suspensions for flow cytometry. All cohorts were conducted thrice.
CD101 expression was increased by high dose LPS inhalation in most cell populations and reduced by enteral antibiotics in splenocytes thereby supporting the hypothesis as CD101 is a recently identified cell surface effector molecule in immune regulation.
FoxP3 expression in Treg and in the total T-helper cell pool was reduced by antibiotics and increased by low dose inhaled LPS, making this a plausible link between LPS exposure and immunomodulation as FoxP3 is the major transcription factor in regulatory T-cells.
High dose, inhaled LPS reversed the increased expression in FoxP3 in the total T-cell population but not in Treg. The high doses also resulted in increased IL-17a expression in the CD4+ splenocytes. Thus the high doses of inhaled LPS appeared to induce a pro-inflammatory milieu.