IgM: mucosal response in acute diarrhoeal disease of infants

Investigating the secretory immune response during the acute phase of diarrhoeal disease is hampered by difficulty in collecting suitable control specimens. This is particularly the case in infants, as they are the most severely affected by this disease. In this study we examined the mucosal immunoglobulin response during the acute phase of diarrhoeal disease in infants.

The intestinal outputs of secretory immunoglobulins (IgA, IgM) and non-secretory proteins (IgG, albumin, A1AT, eosinophil cationic protein (ECP)) were measured in 14 African children with acute watery diarrhoea (less than 3 days). These data were compared with those of 38 controls from the same area who had undergone whole-gut lavage (WGL) (inducing non-pathogenic watery diarrhoea) in a previous study of intestinal immunity and inflammation. Intestinal secretion rates were measured by multiplying the concentration of the substances by the rate of administration of WGL fluid (equal to the output) or by the output of diarrhoea. Statistical comparison was made using the Mann-Whitney U-test.

IgA output in subjects with diarrhoea was 1.8-fold greater (80.7 versus 45.6 mg/kg/day, p=0.03), whereas IgM output was 10-fold greater (21 versus 2.1 mg/kg/day, p=0.0001). Albumin, A1AT and IgG were all also greater to varying degrees (2.5-6.8-fold). ECP was unchanged. Increases in the non-secretory proteins would suggest increased permeability of the gastrointestinal tract but transudation of serum was insufficient to explain the rise in immunoglobulin output.

The 10-fold increase in IgM secretion compared with a smaller relative increase in IgA suggests that this is the primary mucosal immune response in acute diarrhoeal disease.