Sequential appearance of T-cell receptor γδ- and αβ-bearing intestinal intra-epithelial lymphocytes in mice after irradiation

We have previously reported that T-cell receptor (TcR) γδ-bearing T cells precede TcR αβ-bearing T cells in appearance in the thymus after whole-body irradiation. In the present study, the kinetics of appearance of intestinal intra-epithelial lymphocytes (IEL) was examined in mice after whole-body irradiation with a lethal dose of 9.5 Gy or with a sublethal dose of 6 Gy. The number of CD3⁺ IEL decreased to the lowest value 4 days after irradiation with 9.5 Gy, and thereafter increased to half as many as the normal level by day 7. Thy-1⁺TcRαβ^- IEL and Thy^-TcRαβ^-IEL recovered considerably by day 7 after the irradiation, whereas Thy-1⁺TcRαβ⁺ IEL and Thy-1⁺TcRαβ⁺ IEL hardly recovered at this stage. All mice died within 12 days after irradiation with a lethal dose of 9.5 Gy. On the other hand, when irradiation dose was decreased to 6 Gy, all mice survived beyond 40 days after irradiation. Thc number of CD3⁺ IEL recovered to the normal level by 10 days after irradiation with 6 Gy. Consistently with the results in mice irradiated with a lethal dose, the first cells to increase in IEL of mice irradiated with a sublethal dose were TcRγδ ⁺ IEL expressing Thy-1 antigen. The number of Thy-1⁺TcRγδ ⁺ IEL increased to approximately two-fold as many as that in normal mice by day 10, while TcRαβ⁺ IEL began to increase in number from day 20 after irradiation and recovered to the normal level by day 40 after irradiation. Thus, sequential appearance of TcRγδ⁺ and TcRαβ⁺ IEL was evident after irradiation, similar to that seen in the thymus after irradiation. The IEL on day 10 after a sublethal irradiation, which is composed mainly of Thy-1⁺TcRγδ⁺ IEL, exhibited a strong cytolytic activity against P815 in the presence of anti-CD3 mAb, suggesting that the early appearing Thy-1⁺TcRγδ⁺ IEL may play important roles in epithelial immunity at an early stage after irradiation.