Editor—Johnston and Openshaw state that children are born with strong interleukin 4 based (type 2) immune responses and mature to interferon γ based (type 1) responses, and that this process is under genetic and environmental influence.1 They go on to state that asthma and atopy are rising in prevalence and that having older siblings and being exposed to infections promotes the normal maturation of the immune system towards a type 1 response.
This argument fails to take account of the evidence from type 1 diabetes, which is an interferon γ based disease. Type 1 diabetes is rising in incidence in children from Western societies and is commoner in first born children and in the children of the well off.2–4 Infection may have a role in the changing epidemiology of disease, but the evidence contradicts the suggestion that this is due to a failure of normal immune development towards a type 1 response.
Though consistent with current dogma, the conclusion that we should attempt to mimic the effect of childhood infection on the immune system is premature, if not totally flawed, on two counts. Firstly, association, not causation, has been shown,5 and, secondly, the proposed mechanism of action is inconsistent with available evidence.
References
- 1.Johnston SL, Openshaw PJM. The protective effect of childhood infection. BMJ. 2001;322:376–377. doi: 10.1136/bmj.322.7283.376. . (17 February.) [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Patterson CC, Carson DJ, Hadden DR. Epidemiology of childhood IDDM in Northern Ireland 1989-1994: low incidence in areas with highest population density and most household crowding. Northern Ireland Diabetes Study Group. Diabetologia. 1996;39:1063–1069. doi: 10.1007/BF00400655. [DOI] [PubMed] [Google Scholar]
- 3.Bingley P, Douek I, Rogers C, Gale E. Influence of maternal age at delivery and birth order on risk of type1 diabetes in childhood: prospective population based family study. BMJ. 2000;321:420–424. doi: 10.1136/bmj.321.7258.420. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Green A, Gale E, Patterson C. Incidence of childhood-onset insulin dependent diabetes mellitus: the EURODIAB ACE study. Lancet. 1992;339:905–909. doi: 10.1016/0140-6736(92)90938-y. [DOI] [PubMed] [Google Scholar]
- 5.Last JM, editor. Hill's criteria of causation. A dictionary of epidemiology. 3rd ed. Oxford: Oxford University Press; 1995. [Google Scholar]