Development of virus-specific CD4(+) T cells during primary cytomegalovirus infection.

Although virus-specific CD4(+) T cells have been characterized extensively in latently infected individuals, it is unclear how these protective T-cell responses develop during primary virus infection in humans. Here, we analyzed the kinetics and characteristics of cytomegalovirus-specific (CMV-specific) CD4(+) T cells in the course of primary CMV infection in kidney transplant recipients. Our data reveal that, as the first sign of specific immunity, circulating CMV-specific CD4(+) T cells become detectable with a median of 7 days after first appearance of CMV-DNA in peripheral blood. These cells produce the T helper 1 type (Th1) cytokines IFNgamma and TNFalpha, but not the T helper 2 type (Th2) cytokine IL4. In primary CMV infection, the vast majority of these circulating virus-specific T cells have features of recently activated naive T cells in that they coexpress CD45RA and CD45R0 and appear to be in the cell cycle. In contrast, in people who have recovered from CMV infection earlier in life, virus-specific T cells do not cycle and express surface markers characteristic of memory T cells. After the initial rise, circulating virus-specific CD4(+) T cells decline rapidly. During this phase, a strong rise in IgM and IgG anti-CMV antibody titers occurs, concomitant with the reduction of CMV-DNA in the circulation.

CD4dullCD8bright double-positive T-lymphocytes have a phenotype of granzyme Bpos CD8pos memory T-lymphocytes.

BACKGROUND: T-lymphocytes that co-express CD4 and CD8 antigens may be found in small percentages in the peripheral blood of healthy individuals, and have a CD4brightCD8dull phenotype. CD4dullCD8bright T-lymphocytes have been found only in temporal association with some viral infections. METHODS: Four-colour flow cytometric analysis of peripheral blood mononuclear cells from a renal transplant recipient with cytomegalovirus infection was performed. RESULTS: A small but clearly distinguishable subpopulation of CD4dullCD8bright double-positive T-lymphocytes was detected, that exhibited phenotypic characteristics of cytotoxic T-lymphocytes and were granzyme B positive. Furthermore, no naive cells appeared to be present within this subpopulation. CONCLUSIONS: CD4dullCD8bright double-positive T-lymphocytes are enriched for memory and effector cytotoxic T cells.

The CD8+ granzyme B+ T-cell subset in peripheral blood from healthy individuals contains activated and apoptosis-prone cells.

Granzyme B (GrB) has been implicated in induction of apoptosis in target cells. The presence of GrB in peripheral blood CD8+ T cells from healthy individuals was analysed in immunocytochemical and flow cytometric studies. Furthermore, CD8+ GrB- T cells and CD8+ GrB+ T cells were compared regarding phenotypical characteristics and susceptibility to both spontaneous and Fasmediated apoptosis. GrB was expressed by approximately one-fifth of CD8+ T cells. Compared with the CD8+ GrB- T-cell subset, the CD8+ GrB+ T-cell subset contained cells that were relatively more activated and more prone to spontaneous apoptosis. Culturing of cells with immunoglobulin M (IgM) anti-Fas monoclonal antibody had no additional effect on the number of CD8+ GrB+ T cells undergoing apoptosis. We suggest that the presence of CD8+ GrB+ T cells in peripheral blood from healthy individuals results from immune surveillance or contact with infectious agents, and that spontaneous apoptosis of these cells might serve as a mechanism for their eventual clearance.

Quantification of Bax/Bcl-2 ratios in peripheral blood lymphocytes, monocytes and granulocytes and their relation to susceptibility to anti-Fas (anti-CD95)-induced apoptosis.

Neutrophils have the shortest half-life among circulating leucocytes and rapidly undergo apoptosis in vitro. The homologous Bcl-2 and Bax proteins have opposing effects, with Bcl-2 extending cellular survival and Bax promoting cell death following an apoptotic stimulus. We determined Bcl-2 to Bax expression ratios in peripheral blood lymphocytes, monocytes and granulocytes and related them to the susceptibility of these cells to anti-Fas (anti-CD95)-induced apoptosis. Here, we show that Bax/Bcl-2 ratios are high in granulocytes and relatively low in monocytes and lymphocytes. Furthermore, we show a relation between this ratio in the different leucocyte subsets and their susceptibility to anti-Fas-induced apoptosis, with granulocytes showing the highest susceptibility, followed by monocytes and lymphocytes. It is concluded that the balance between Bcl-2 and Bax forms an apoptotic rheostat, which seems to determine sensitivity to apoptosis.

Administration of OKT3 as a two-hour infusion attenuates first-dose side effects.

BACKGROUND: Use of the murine CD3 monoclonal antibody OKT3 is limited by first-dose side effects, which are thought to be caused by the release of inflammatory mediators. Because these processes might be influenced by the speed of administration, we compared a 2-hr OKT3 infusion with the bolus infusion usually applied nowadays. METHODS: Eighteen renal allograft recipients were prophylactically treated with OKT3 and randomized to receive the first dose either as a 2-hr infusion or as an intravenous bolus infusion. Clinical side effects score and the occurrence of complement activation, cytokine release, and activation of neutrophils were determined. RESULTS: Two-hour infusion of OKT3 completely prevented the occurrence of dyspnea, reduced the incidence of other side effects, and attenuated complement activation. Cytokine release and depletion of peripheral blood lymphocytes were similar in both groups. CONCLUSIONS: Thus, complement activation seems to play an additional role in the development of side effects after the first OKT3 dose.

Increased dermal expression of ICAM-1 and VCAM-1 after administration of OKT3 in man.

OKT3 induces a systemic release of cytokines and a profound peripheral lymphocytopenia. In vitro, tumor necrosis factor-alpha, interleukin-1, and interferon-gamma increase adhesion molecule expression on vascular endothelium. To investigate the effects of OKT3 induced cytokine release on endothelial- and lymphocyte adhesion molecule expression in vivo, we studied sequential skin biopsies of six renal allograft recipients treated for acute rejection with 5 mg OKT3. An additional group of six patients treated for acute rejection with 50 mg methylprednisolone served as a control group. Compared to pre-treatment biopsies, biopsies taken 4.5- and 24 hours after the first OKT3 dose showed a maximal increase in VCAM-1 and ICAM-1 expression, respectively. In parallel, an increased number of CD2+, CD11a+, and CD49d+ mononuclear cells in the skin was observed in all OKT3 treated patients. No changes were observed after methylprednisolone treatment. We conclude that the OKT3 induced cytokine release induces increased ICAM-1- and VCAM-1 expression on vascular endothelium, leading to increased influx of CD2+ lymphocytes which may contribute to the peripheral lymphocytopenia after OKT3.

Biphasic granulocytopenia after administration of the first dose of OKT3.

The effects of the administration of OKT3, a second immunoglobulin G2a (IgG2a) anti-CD3 monoclonal antibody (mAb), and its isotype switch variant IgA on granulocyte kinetics were compared for 5 hours after the first administration of the mAb. In addition, in vivo and in vitro studies were performed on alterations in expression of CD11b and CD62L induced by these mAbs. Within 15 minutes after administration OKT3 and IgG2a anti-CD3 mAbs induced a significant decrease in circulating granulocytes, whereas IgA anti-CD3 mAb did not. Apparently the initial decrease in circulating granulocytes depends on the heavy chain of the administered anti-CD3 mAb, resulting in immunocytoadherence and sequestration in the lungs. Increased adherence to pulmonary endothelium by altered expression of CD11b and CD62L plays a minor role in this first granulocytopenia, because each mAb exerted the same effects on these adhesion molecules in vitro. The second decrease in granulocyte counts occurred 60 minutes after administration of each mAb and correlated with a significant increase in expression of CD11b and CD62L in vivo and with upregulation of CD11b and down-regulation of CD62L in vitro. These alterations could be related to the presence of tumor necrosis factor-alpha both in vivo and in vitro. Thus granulocyte kinetics from 30 minutes after administration of each anti-CD3 mAb resemble neutrophil kinetics induced by TNF-alpha.

Complement activation during OKT3 treatment: a possible explanation for respiratory side effects.

Respiratory side effects that sometimes occur during treatment with anti-CD3 MAb OKT3 might result from pulmonary sequestration of activated neutrophils. Therefore, we studied complement activation in relation to activation and pulmonary sequestration of neutrophils during antirejection treatment with OKT3. In each of nine patients studied, plasma C3a-desarg and C4b/c levels increased compared with pretreatment values already in the first sample taken 15 minutes after the first dose of OKT3 (P < 0.05), with peak values at 15 and 30 minutes, respectively. Levels of neutrophil degranulation product elastase (complexed to alpha 1-antitrypsin) also increased already at 15 minutes after the first dose of OKT3 (P < 0.05), which is before elevated levels of the cytokines TNF alpha, IL-6 or IL-8 were detectable. In contrast, upon subsequent OKT3 administrations or in the control group treated with methylprednisolone, neither complement activation, cytokine release nor neutrophil degranulation occurred. In five studied patients treated with OKT3, pulmonary sequestration of radiolabeled granulocytes was observed from 3 until 15 minutes after the first dose of OKT3, together with peripheral blood granulocytopenia, which lasted at least 30 minutes. In conclusion, we demonstrate a simultaneous activation of complement and pulmonary sequestration of activated granulocytes immediately following the first dose of OKT3. These phenomena may be involved in the development of respiratory side effects complicating this therapy.