The significance of cytokine production by CD4+ regulatory T (T reg) cells after antigen exposure in vivo and its impact on their regulatory activity remains unclear. Pretreatment with donor alloantigen under the cover of anti-CD4 therapy generates alloantigen reactive T reg cells that can prevent rejection of donor-specific skin grafts that are mediated by naive CD45RBhighCD4+ T cells. To examine the kinetics and importance of cytokine gene transcription by such alloantigen-reactive T reg cells, pretreated mice were rechallenged with donor alloantigen in vivo. CD25+CD4+ T cells, but not CD25−CD4+ T cells, showed a fivefold increase in IFN-γ mRNA expression within 24 h of reencountering alloantigen in vivo. This expression kinetic was highly antigen-specific and was of functional significance. Neutralizing IFN-γ at the time of cotransfer of alloantigen reactive T reg cells, together with CD45RBhighCD4+ effector T cells into Rag −/− skin graft recipients, resulted in skin graft necrosis in all recipients; the generation and function of alloantigen-reactive T reg cells was impaired dramatically in IFN-γ–deficient mice. These data support a unique role for IFN-γ in the functional activity of alloantigen-reactive T reg cells during the development of operational tolerance to donor alloantigens in vivo.

Blockade of CD40-CD154 interactions can facilitate long-term allograft acceptance in selected rodent and in primate models, but, due to the ability of CD154-independent CD8(+) T cells to initiate graft rejection, this strategy is not always effective. In this work we demonstrate that blockade of the CD40-CD154 pathway at the time of transplantation enables the generation of donor alloantigen-specific CD4(+)CD25(+) regulatory T cells, and that if the regulatory cells are present in sufficient numbers they can suppress allograft rejection mediated by CD154-independent CD8(+) T cells.

SUMMARYIn atopic patients and patients with hyper-IgE syndrome (HIE) highly elevated IgE serum levels can be detected. Due to their very low frequency little is known about IgE-producing plasma cells (PC) in peripheral blood. We used CD138 MACS microbeads to enrich plasma cells from peripheral blood of normal donors, atopic patients and one HIE patient. CD138 + cells were mainly CD45 + , CD44 ++ , CD19 dim , CD38 ++ , CD27 ++ , CD86 + , HLA-DR + / ++ , CD71 dim , VLA-4 + , VLA-5 -, CD28 -, CD25 -, CD69 -, CLA -, CD20 -, CD21 -and CD22 -. They show weak expression of surface Ig but high levels of intracellular Ig and they secrete Ig in culture. Thus CD138 + cells from peripheral blood show characteristics of early plasma cells. IgE + CD138 + plasma cells could be detected in 19 of 24 normal donors with an average frequency of 0·06% IgE + cells among CD138 + cells. Higher frequencies were detected in atopic patients, atopic patients with markedly elevated serum IgE levels and the hyper-IgE patient with an average of 0·32%, 7·21% and 6·54%, respectively. Additionally, using the recently developed cellular affinity matrix technology, we were able to detect IgE secreting plasma cells and thereby could demonstrate that most of the IgE secreting cells express CD138. The frequency of IgE + CD138 + cells among PBMC correlated highly significantly with serum IgE titres ( r = 0·8532***), indicating that IgE secreting CD138 + cells in peripheral blood are directly related to the plasma cell pool contributing to the IgE titre.