Disease can occur when immunity is low or impaired when virulence of the pathogen its ability to damage host cells is high and when the number of pathogens in the body is great depending on the infectious disease symptoms can vary greatly. The immune system and infectious disease carl nathan studies the workings of the bodys immune system in relation to infectious diseases with a focus on tuberculosis as a model featured carl f nathan ra rees pritchett professor of microbiology weill cornell medicine . Immunity in infective diseases by elie metchnikoff e metchnikoff publication date 1905 publisher university press collection americana digitizing sponsor google book from the collections of harvard university language english. There are various types of b cells each of which can produce only one of the five known forms of immunoglobulin ig the first immunoglobulin to be produced is igm later during recovery from infection the immunoglobulin igg which can specifically kill the invading microorganism is produced