Ex­po­sure v pro­tec­tion

Build­ing im­mu­nity may be a mat­ter of keep­ing com­pany with mi­crobes, ar­gue some im­mu­nol­o­gists


Should chil­dren be brought up in sani­tised sur­round­ings? Or should they be ex­posed to dirt to de­velop im­mu­nity?

YOU THINK IT'S all right to eat food off the floor? Or are you one of those whose mod­ern fear of all ver­min ren­ders the idea sick­en­ing? For a long time, peo­ple have been given to un­der­stand that it is sci­en­tif­i­cally kosher to re­trieve “fallen” food pro­vided it was not in con­tact with the floor for more than five sec­onds. Now a new study ques­tions this thumb-rule, claim­ing that if the food is moist, such as but­tered toast, harm­ful bac­te­ria can latch on it within a sec­ond.

The study, au­thored by Don­ald Schaffner, pro­fes­sor at Rut­gers Univer­sity, did not in­ves­ti­gate whether eat­ing floor-kissed foods ac­tu­ally makes peo­ple sick. For, to be sure, many with a slightly re­laxed sense of hy­giene in­dulge in this risky be­hav­iour, which may or may not re­sult in ill­ness. Nonethe­less, it does sug­gest that as a gen­eral rule you are safer trash­ing the dropped bits, no mat­ter how tempt­ingly de­li­cious.

This should most likely ap­ply to adults but should kids too fol­low this pre­scrip­tion? Cu­ri­ously enough no, if you put your bets on the hy­giene hy­poth­e­sis, which sug­gests that the de­cline in in­fec­tious dis­eases in the West through bet­ter hy­giene and san­i­ta­tion, which in­evitably led to a mass purg­ing of mi­crobes from hu­man habi­tats, is prob­a­bly be­hind the al­most par­al­lel rise in new and mostly ur­ban af­flic­tions such as al­ler­gies and au­toim­mune dis­eases.

First pro­posed in 1989 by a Bri­tish epi­demi­ol­o­gist, David Stra­chan, the ba­sic idea be­hind the hy­poth­e­sis is sim­ple. The im­mune sys­tem of ba­bies yet to see the light of the day is weak, pro­tected as they are by the mother’s body­guards. To pro­tect their im­mune sys­tems from the dan­gers of an alien world, ba­bies once de­liv­ered must be al­lowed to bathe in the nat­u­ral shower of germs, pro­po­nents be­lieve. This boosts im­mu­nity, they claim, even though they are not sure how. More re­cent ver­sions sug­gest there are two kinds of body­guards. If one of them is not trained well, the other be­comes over-sen­si­tive, thus caus­ing al­ler­gic or au­toim­mune re­ac­tions.

The hy­poth­e­sis seemed counter-in­tu­itive when it was pro­posed the first time, but over the past two decades it has gained cur­rency thanks to stud­ies back­ing its premise. Epi­demi­ol­o­gists have shown that chil­dren reared in the coun­try, and hence less clean sur­round­ings, are far less prone to al­ler­gies and au­toim­mune glitches than their ur­ban cousins. An oft-quoted study found that chil­dren brought up in dirt­ier East Ger­many were iron­i­cally much less vul­ner­a­ble to al­ler­gies and asthma than chil­dren grow­ing up in sani­tised West Ger­many. Stud­ies have found sim­i­lar as­so­ci­a­tions be­tween the de­vel­op­ing and the de­vel­oped world. In the past two years, im­mu­nol­o­gists have also un­rav­elled a few nuts and bolts un­der­pin­ning the hy­poth­e­sis. Last month a Tech­ni­cal Univer­sity of Mu­nich study on mice pro­posed that “if it is pos­si­ble to en­cour­age harm­less bac­te­ria to colonise the in­testines, this would also re­duce the body’s re­ac­tion to al­ler­gens”. Another study by the Pas­teur In­sti­tute in France demon­strates how mi­crobes sab­o­tage im­mune cells im­pli­cated in al­ler­gic re­ac­tions.

The hy­poth­e­sis is a work-in-progress, but as the body of ev­i­dence grows, it is bound to at­tract more ad­her­ents. At any rate, it has al­ready cap­tured pop­u­lar imag­i­na­tion. The grow­ing aver­sion to vac­ci­na­tion, an­tibi­otics and C-section, all of which im­pov­er­ish the baby of its mi­cro­bial heir­loom, point to the grow­ing ap­peal of the hy­poth­e­sis. Some moth­ers, who for some rea­son can­not de­liver nat­u­rally, even want their ba­bies smeared with their vagi­nal flu­ids! A new book, Let them eat dirt, ar­gues against fetishis­ing clean­li­ness when it comes to par­ent­ing. Even so, this presents a frus­trat­ing dilemma—pro­tect­ing ver­sus ex­pos­ing—for par­ents sym­pa­thetic to this rad­i­cal no­tion. Re­ject­ing vac­cines and an­tibi­otics might be tricky, but they can at least al­low the kids to wal­low in dirt.

That said, a ro­bust im­mu­nity is prob­a­bly as much about keep­ing com­pany with mi­crobes as about eat­ing nu­tri­tious food, sleep­ing well, be­sides much else. As in all things, here too mod­er­a­tion is per­haps the key.


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