Larger than life - he stood six foot three - Professor John Soothill, who has died aged 79, must have seemed to a sick child at London's Great Ormond Street hospital like Roald Dahl's Big Friendly Giant striding the wards. But this BFG, the Hugh Greenwood professor of immunology, had come in search of hidden enemies, a food they liked yet should not have, or a lurking virus to be cornered.
To the hundreds of medical students from across the world, whom he taught at Great Ormond Street from 1965 to 1985, he was at first encounter certainly not friendly, more formidable, demanding their utter attention with his booming baritone onslaught of questions and ideas. He would insist they enunciate their thesis paper with clear BBC authority - as one timorous student, later to become a friend and successor to his office, agreed: "After all, we were the ambassadors for his department." Yet once they settled to his task, they came to recognise a generous, if eccentric, doctor, always sharing his flow of ideas.
From Great Ormond Street, his pioneering work in food allergies took him across the world conference circuit. He established his theory that the onset of an allergy is due to exposure to an allergic substance at a vulnerable period when the immune system is maturing in the first six months of a baby's life.
As well as his research and clinical work, his appetite for teaching generations of students knew few international bounds. During one of his dreaded Tuesday ward rounds during which he would bombard junior doctors with novel ideas and questions, most hung back, hoping to stay out of his firing range. On one such round, when a young South African student sneezed, he immediately diagnosed hay fever. Bolder than most, the junior doctor disagreed, reminding his professor that it was midwinter. "'But haven't you forgotten," John replied, "you were born in South Africa, where the seasons are reversed."
He would invite students to parties in his Hampstead home where they would meet his friends, many of them distinguished medics; then he would encourage them to explain their work. Among past students are numbered three vice-chancellors and over 30 professors, while many of his students went on to set up departments in their home countries.
John was the son of a medical officer of health in Norwich; his grandfather, a missionary in China, came home to become the first Oxford professor of sinology. Educated at Leys school, Cambridge - evacuated to Scotland during the war - boyhood holidays on the Norfolk Broads meant sailing. John read medicine at Christ's College Cambridge in the mid-1940s, where he took to climbing, notably around Pitlochry, his favourite Scottish challenge, perhaps to escape the bane of his life, dyslexia. He completed his medical qualifications at Guy's Hospital, and after national service, a Fulbright Scholarship took him in 1955 for a fruitful year in Chicago.
On his return in 1956, he settled into Birmingham University's department of experimental pathology with a special interest in renal disease. Then, after nine years, his teaching and research were such that, in 1965, he was summoned to Great Ormond Street.
Retiring in 1985 to Devon with his wife - a professional violinist - John settled into a rural routine of tending his farmhouse and two-acre garden and pursuing his lifelong love of music. His baritone voice, already the familiar of Schubert songs, now moved on to the English madrigal, and he started his own singing group.
His boyhood love of sailing returned as he launched his dayboat from Lyme Regis and indulged in his lifelong comforts - Milton, Eliot and above all Shakespeare, large swathes of whom he was able to quote by heart. He is survived by his wife Brenda, their daughter and three sons.
· John Soothill, immunologist and paediatrician, born August 20 1925; died September 23 2004
