Early T cell depletion occurs prior to the development of an effective immune response to infections.Both antigen-specific and non-specific T cells are induced to express early activation markers soon after microbial infections.This is followed by massive depletion of non-specific T cells and extensive proliferation of antigen-specific T cells.Proliferating antigen-specific cells exhibit a broad spectrum of late activation markers while non-specific cells exhibit no sign of further activation before succumbing to apoptosis.These results have crucial implications for the understanding of early events in the development of a robust T cell response. Depletion of lymphocytes has been observed in the early stage of bacterial and viral infections [1～3].This early T cell depletion is often associated with a transient,generalized immunosuppression but is followed by an effective antigen-specific T cell response that controls infection.The significance of this depletion as well as early events of the T cell response remains largely unknown.The observation of early T cell depletion has been well characterized during Listeria monocytogenes(LM) infection [3～7].More than 90% of splenic T cells were depleted between 48-72 h after LM infection and this massive depletion of T lymphocytes was not due to altered trafficking [4～7] but due to in situ death by apoptosis [7].Attrition of bystander memory T cells following heterologous viral infections has been well documented [2,8,9].Recent studies have also shown extensive depletion of bystander naive T cells during the early stage of viral infection [1].However,it is still not known whether depletion involves only bystander T cells or includes both antigen-specific and non-specific T cells.The significance of bystander T cell depletion remains unknown and puzzling in the case of memory T cells since it leads to diminished CD8 T cell memory and protective immunity.In a recent study [10],we observed that most T cells,regardless of specificity,were activated to express early activation markers rapidly after LM infection.This was followed by selective depletion of non-specific cells and huge expansion of antigen-specific T cells.Confocal microscopy demonstrated that this depletion was due to in situ death of non-specific T cells.This phenomenon of early T cell activation and subsequent depletion of non-specific T cells was also observed following LCMV infection.The study was summarized as follows: Selective depletion of non-specific T cells during LM infection Early T cell depletion occurs prior to the development of an effective immune response to infections. Both antigen-specific and non-specific T cells are induced to express early activation markers soon after microbial infections. This is followed by massive depletion of non-specific T cells and extensive proliferation of antigen-specific cells exhibit a broad spectrum of late activation markers while non-specific cells exhibit no sign of further activation before succumbing to apoptosis. These results have crucial implications for the understanding of early events in the development of a robust T cell response. Depletion of lymphocytes has been observed in the early stage of bacterial and viral infections [1 ~ 3]. This early T cell depletion is often associated with a transient, generalized immunosuppression but is followed by an effective antigen-specific T cell response that controls infection. The significance of this depletion as well as early event s of the T cell response remains largely unknown. The observation of early T cell depletion has been characterized during Listeria monocytogenes (LM) infection [3-7]. More than 90% of splenic T cells were depleted between 48-72 h after LM infection and this massive depletion of T lymphocytes was not due to altered traslations [4-7] but due to in situ death by apoptosis [7]. Attrition of bystander memory T cells following heterologous viral infections has been well documented [2, 8 , 9] .Recent studies have also shown extensive depletion of bystander naive T cells during the early stage of viral infection [1]. However, it is still not known whether depletion involves only bystander T cells or includes both antigen-specific and non- specific T cells. The significance of bystander T cell depletion remains unknown and puzzling in the case of memory T cells since it leads to diminished CD8 T cell memory and protective immunity. In a recent study [10], we observed that most T cells, regardless of specificity, were activated to express early activation markers rapidly after LM infection. This was followed by selective depletion of non-specific cells and huge expansion of antigen-specific T cells. Confocal microscopyiform that said depletion was due to in situ death of non- specific T cells. This phenomenon of early T cell activation and subsequent depletion of non-specific T cells was also observed LCMV infection. The study was summarized as follows: Selective depletion of non-specific T cells during LM infection