Immunity & infection
We have recently reported on the accumulation of plasma cells (PCs) in the human thymus, starting several months after birth. This thymic PC niche includes clones specific to common viruses presumably generated through peripheral responses. Humans acquire humoral immunity to dietary antigens during the first 3 years of life. Here we investigated whether such immunity also resulted in the homing of specific PC to the thymus. Using ELISPOT assays, we tested for the presence of antibody-producing cells specific to known immunogenic food antigens among B cells isolated from discarded thymus specimens from 1 day to 3 years patients. Results revealed the presence of PC specific to cow’s milk, egg and wheat derived antigens in 2 out of 10 patients. Furthermore, the presence of thymic food antigen-specific PC was associated with high serum IgG titers to same antigens, indicative of an ongoing immune response. Our study demonstrates for the first time the presence of antibody-secreting cells specific to antigen towards which tolerance is usually established and maintained, in the thymic of human infants. Their role and possible contribution to T cell education warrant further investigation.