Affinity maturation of antibodies requires integrity of the adult thymus.

The generation of B-cell responses to proteins requires a functional thymus to produce CD4(+) T cells which helps in the activation and differentiation of B cells. Because the mature T-cell repertoire has abundant cells with the helper phenotype, one might predict that in mature individuals, the generation of B-cell memory would proceed independently of the thymus. Contrary to that prediction, we show here that the removal of the thymus after the establishment of the T-cell compartment or sham surgery without removal of the thymus impairs the affinity maturation of antibodies. Because removal or manipulation of the thymus did not decrease the frequency of mutation of the Ig variable heavy chain exons encoding antigen-specific antibodies, we conclude that the thymus controls affinity maturation of antibodies in the mature individual by facilitating the selection of B cells with high-affinity antibodies.

TLR2 and TLR4 expression on blood monocytes and granulocytes of cardiac surgical patients is not affected by the use of cardiopulmonary bypass.

Cardiac surgery is inseparably linked to the activation of innate immunity cells recognizing danger signals of both endogenous and exogenous origin via pattern recognition receptors such as TLR receptors. Therefore, we followed by flow cytometry TLR2 and TLR4 expression on blood monocytes and granulocytes of patients who underwent coronary artery bypass grafting using beating heart surgery (off-pump, n = 34), with use of standard cardiopulmonary bypass (CPB), (on-pump, n = 30), and miniinvasive CPB (mini on-pump, n = 25), respectively, before, during surgery, and up to 7th postoperative day. TLR2 and TLR4 expression both on monocytes and granulocytes was significantly diminished already at the end of CPB being highly significantly decreased at the end of surgery in all patients' groups. TLR2 and TLR4 expression reached preoperative value at the 1st postoperative day being significantly higher at the 3rd postoperative day. Using intracellular staining we found the peak of TLR2 and TLR4 expression inside of monocytes and granulocytes at the first postoperative day in a subgroup of on-pump patients. In conclusion, TLR2 and TLR4 expression is significantly modulated in patients undergoing coronary artery bypass grafting as a part of adaptive homeostatic mechanisms induced by major surgery. The very surgical trauma is responsible for TLR2 and TLR4 modulation. Surprisingly, cardiopulmonary bypass itself was little contributing to the modulation of TLR2 and TLR4 expression.

Fitness of cell-mediated immunity independent of repertoire diversity.

Fitness of cell-mediated immunity is thought to depend on TCR diversity; however, this concept has not been tested formally. We tested the concept using JH(-/-) mice that lack B cells and have TCR Vbeta diversity <1% that of wild-type mice and quasimonoclonal (QM) mice with oligoclonal B cells and TCR Vbeta diversity 7% that of wild-type mice. Despite having a TCR repertoire contracted >99% and defective lymphoid organogenesis, JH(-/-) mice rejected H-Y-incompatible skin grafts as rapidly as wild-type mice. JH(-/-) mice exhibited T cell priming by peptide and delayed-type hypersensitivity, although these responses were less than normal owing either to TCR repertoire contraction or defective lymphoid organogenesis. QM mice with TCR diversity contracted >90%, and normal lymphoid organs rejected H-Y incompatible skin grafts as rapidly as wild type mice and exhibited normal T cell priming and normal delayed-type hypersensitivity reactions. QM mice also resisted Pneumocystis murina like wild-type mice. Thus, cell-mediated immunity can function normally despite contractions of TCR diversity >90% and possibly >99%.