Validity of the two-signal model for activation of CD28-deficient T lymphocytes: quantitative characterization of an alternative costimulatory function of dendritic cells.

The observation that primary T-dependent immune responses are generated in mice lacking CD28, the only receptor definitively shown to costimulate naive T cells, has led to ambiguity as to whether costimulation is absolutely required for initiation of T-cell responses. In this report, in vitro analysis of the relationship between cell density and proliferation demonstrates that activation of CD28-/- T cells to immobilized T-cell receptor (TCR)-alpha monoclonal antibodies (MoAb) depends on costimulatory signals provided by other cells in culture and occurs only at cell densities sufficient to permit these intercellular interactions. These signals are necessary even under TCR triggering conditions that obviate the CD28 requirement. Dendritic cells (DCs) provide the necessary costimulation in vitro and prime T cells in vivo in CD28-/- mice. Single-cell and limiting dilution analyses indicate that individual T cells from normal and CD28-/- mice produce equivalent interleukin (IL)-2 in response to DCs. However, half as many T cells produce IL-2 when only the CD28-independent pathway is used. Nonetheless, CD28-/- T cells produce sufficient IL-2 to support clonal expansion comparable to that of CD28+/+ T cells, which may account for the equally robust in vivo responses initiated by DCs in normal and CD28-deficient animals.

Assessment of myocardial viability by dynamic tomographic iodine 123 iodophenylpentadecanoic acid imaging: comparison with rest-redistribution thallium 201 imaging.

BACKGROUND: This study examined the ability of dynamic 123I-labeled iodophenylpentadecanoic acid (IPPA) imaging to detect myocardial viability in patients with left ventricular (LV) dysfunction caused by coronary artery disease. METHODS AND RESULTS: Serial 180-degree single-photon emission computed tomographic (SPECT) images (five sets, 8 minutes each) were obtained starting 4 minutes after injection of 2 to 6 mCi 123I at rest in 21 patients with LV dysfunction (ejection fraction [EF] 34% +/- 11%). The segmental uptake was compared with that of rest-redistribution 201Tl images (20 segments/study). The number of perfusion defects (reversible and fixed) was similar by IPPA and thallium (11 +/- 5 vs 10 +/- 5 segments/patient; difference not significant). There was agreement between IPPA and thallium for presence or absence (kappa = 0.78 +/- 0.03) and nature (reversible, mild fixed, or severe fixed) of perfusion defects (kappa = 0.54 +/- 0.04). However, there were more reversible IPPA defects than reversible thallium defects (7 +/- 4 vs 3 +/- 4 segments/patient; p = 0.001). In 14 patients the EF (by gated pool imaging) improved after coronary revascularization from 33% +/- 11% to 39% +/- 12% (p = 0.002). The number of reversible IPPA defects was greater in the seven patients who had improvement in EF than in the patients without such improvement (10 +/- 4 vs 5 +/- 4 segments/patient; p = 0.075). CONCLUSIONS: 123I-labeled IPPA SPECT imaging is a promising new technique for assessment of viability. Reversible defects predict recovery of LV dysfunction after coronary revascularization.

Serial changes in left ventricular function after coronary artery bypass: implications in viability assessment.

Improvement in left ventricular (LV) performance after coronary artery bypass surgery remains the gold standard in myocardial viability assessment. The time-related changes, however, are not well known. This study examined the LV ejection fraction (EF) by gated blood pool imaging early (6 +/- 4 days) and late (62 +/- 24 days) after surgery in patients with normal preoperative EF (group 1, n = 12) and those with LV dysfunction (group 2, n = 15). There were no changes in the clinical status between the early and late studies, and all patients had normal sinus rhythm. Group 1 had no significant change in EF (preoperatively 62%, early postoperatively 64%, late postoperatively 63%; p = NS). In group 2, EF was 26% +/- 8% preoperatively; 30% +/- 10% early postoperatively; and 34% +/- 8% late postoperatively (p < 0.05). Postoperatively there was > or = 5% improvement in EF in 4 patients early and 11 patients late (p < 0.05). Patients who showed early improvement continued to do so in the late study but, additionally, 7 patients showed improvement only in the late study. Thus the timing of EF measurement after surgery is important in patients with LV dysfunction but not in patients with normal LV function. Early assessment may underestimate the prevalence and degree of recovery.

A quantitative analysis of antigen-presenting cell function: activated B cells stimulate naive CD4 T cells but are inferior to dendritic cells in providing costimulation.

Ligation of CD28 on CD4 Th1 clones and freshly isolated mixtures of naive and memory CD4 T cells triggered their T cell receptors (TCR) is sufficient to induce the costimulatory signals necessary for interleukin 2 (IL-2) production by these cells. CTLA-4-reactive ligands expressed on antigen-presenting cells (APC) are critical in providing costimulatory signals to these T cell populations. We demonstrate that these activation characteristics apply equally to purified naive CD4 T cells. Because B cell blasts express CTLA-4-reactive ligands and high levels of adhesion and major histocompatibility complex class II molecules, they would be expected to engage both the TCR and CD28 and consequently stimulate IL-2 production by naive CD4 T cells. Using purified populations of cells in limiting dilution cultures, we have carried out a quantitative analysis of the interaction between naive CD4 T cells and either activated B or dendritic cells. We demonstrate that B cell blasts stimulate a high frequency of naive CD4 T cells. Slight differences in TCR signaling efficiency between the two APC types were observed. Even at optimal peptide concentrations, however, the amount of IL-2 made by individual T cells was fourfold lower in response to B cell blasts than to dendritic cells. This relative deficiency of activated B cells was due to their inability to optimally costimulate naive CD4 T cells.

Effects of three colors in an office interior on mood and performance.

This study examined the effects of three hues on subjects' performance and mood while in an office work environment for 1 hour. Pretest/posttest measurements were completed. Work performance was measured using words typed, typing errors, and a ratio of errors to words typed. Anxiety, depression, and arousal were measured by the Eight State Questionnaire of Curran and Cattell. A total of 45 women, ages 18 to 24 years, were tested individually in a single office space: 15 when the office walls were painted red/warm, 15 when walls were blue-green/cool, and 15 when walls were white/neutral. Analysis of covariance of posttest measurements with the pretest as a covariate showed no significant differences among the three groups on performance or scores on anxiety, depression, and arousal. If color of the environment has an effect on work performance or mood, either the effect was too small to be detected with samples of 15 subjects or longer participation than one hour was required.

Two roles for CD4 cells in the control of the generation of cytotoxic T lymphocytes.

The generation of CTL against Qa-1 Ag in C57BL/6 (B6) (Qa-1b) and B6.Tlaa (Qa-1a) congenic strains requires in vivo priming with the Qa-1 alloantigen together with a helper Ag, such as H-Y. The primed precursors obtained from these female mice generate Qa-1-specific CTL activity upon culture in vitro. Although the presence of the H-Y helper Ag is not required for the in vitro sensitization, no response occurs in the absence of CD4 cells. Addition of unprimed B6.Tlaa CD4 cells from Qa-1 incompatible radiation bone marrow chimeras (B6.Tlaa----B6), that are presumably tolerant to Qa-1b, provide helper activity for Qa-1b-specific CTL. This indicates that although CD4 cells are obligatory for the Qa-1 response, they need not be specific for alloantigens on the APC to generate helper activity in in vitro cultures. Addition of unirradiated B6 CD8-depleted spleen cells to CD4-depleted B6.Tlaa anti-B6 cultures in the presence of either B6.Tlaa CD4 cells or rIL-2 prevents the generation of Qa-1 specific CTL. This inhibition is not due to an anti-idiotypic Ts cell since B6.Tlaa----B6 chimeric cells do not suppress an anti-Qa-1b response. Rather, this finding is consistent with that of a veto cell mechanism. To determine whether CD4 cells themselves exhibit veto activity, highly purified CD4 populations were tested for their ability to inhibit the generation of Qa-1-specific CTL. CD4 cells precultured for 2 to 3 days with Con A and rIL-2 specifically inhibit CTL activity whereas resting cells do not, similar to that noted for CD8 veto cells. The relative efficiency of activated CD4 cells is greater than that of resting NK cells but is less than that of activated CD8 or NK cells. Thus, CD4 cells not only provide helper activity for CTL precursors, but also act as veto cells to prevent the generation of CTL activity.

Regulation of the cytotoxic T lymphocyte response against Qa-1 alloantigens.

Spleen cells from B6.Tlaa (Qa-1a) mice primed against C57BL/6 (Qa-1b) splenocytes in vivo generate Qa-1-specific CTL when rechallenged with Qa-1b Ag in vitro. The addition of unirradiated Qa-1b splenocytes to these cultures inhibits the generation of Qa-1-specific CTL. By using highly purified cell populations, we demonstrate that the only cell population in resting spleen capable of causing this inhibition is NK1.1+. Although resting CD8 cells lack inhibitory activity, purified CD8 cells precultured with Con A and IL-2 inhibit anti-Qa-1 CTL. This inhibition is specific for the Qa-1b Ag expressed on the inhibitor cells, is not due to cold target competition, and is thus similar to that ascribed to veto cells. Although NK cells from resting spleen inhibit the generation of Qa-1-specific CTL, NK cells precultured in the presence of Con A and IL-2 show an approximate 30-fold increase in veto activity. Thus, NK cells represent the most likely cell population for down-regulating anti-self class I-reactive CTL.