Spectral sensitivity study of dose distributions for a commercial convolution/superposition algorithm

The focus of this study is to validate whether the sensitivity of dose distribution following the interface of different media can be used to distinguish between small variations of photon energy spectra in the context of the convolution/superposition algorithm in the polyenergetic implementation (Philips Pinnacle3, ADAC Laboratories, Milpitas, CA). Calculations were performed in homogeneous water and heterogeneous lung/water phantoms. Spectra were generated, in which the weights of the low-, medium- and high-energy components were adjusted sequentially. The heterogeneity correction factor CFlung, the D20/D10 ratio for homogeneous water and logarithmic derivative in buildup region LDbuildup were assessed for their relative ability to discriminate between different spectra for various field sizes. In accordance with another study (Charland et al 2004), the superior discrimination ability of the CFlung and LDbuildup tests over the D20/D10 test was observed for changes in an energy component as small as 0.3% of the total weight in the energy spectrum. Furthermore, new tests utilizing transverse dose profile data for discriminating between spectra, Fringe Index (FI) and Penumbra Index (PI), were introduced. The discrimination ability of the PI and FI tests was superior when a medium containing interface effects was exploited to obtain the transverse profile data (water/lung phantom for PIhung and FIlung tests) as opposed to when a homogeneous water medium was used (PIwater and FIwater tests).

Biochemical Differences in the αβ T Cell Receptor·CD3 Surface Complex between CD8+ and CD4+ Human Mature T Lymphocytes

We have reported the existence of biochemical and conformational differences in the alphabeta T cell receptor (TCR) complex between CD4(+) and CD8(+) CD3gamma-deficient (gamma(-)) mature T cells. In the present study, we have furthered our understanding and extended the observations to primary T lymphocytes from normal (gamma(+)) individuals. Surface TCR.CD3 components from CD4(+) gamma(-) T cells, other than CD3gamma, were detectable and similar in size to CD4(+) gamma(+) controls. Their native TCR.CD3 complex was also similar to CD4(+) gamma(+) controls, except for an alphabeta(deltaepsilon)(2)zeta(2) instead of an alphabetagammaepsilondeltaepsilonzeta(2) stoichiometry. In contrast, the surface TCRalpha, TCRbeta, and CD3delta chains of CD8(+) gamma(-) T cells did not possess their usual sizes. Using confocal immunofluorescence, TCRalpha was hardly detectable in CD8(+) gamma(-) T cells. Blue native gels (BN-PAGE) demonstrated the existence of a heterogeneous population of TCR.CD3 in these cells. Using primary peripheral blood T lymphocytes from normal (gamma(+)) donors, we performed a broad epitopic scan. In contrast to all other TCR.CD3-specific monoclonal antibodies, RW2-8C8 stained CD8(+) better than it did CD4(+) T cells, and the difference was dependent on glycosylation of the TCR.CD3 complex but independent of T cell activation or differentiation. RW2-8C8 staining of CD8(+) T cells was shown to be more dependent on lipid raft integrity than that of CD4(+) T cells. Finally, immunoprecipitation studies on purified primary CD4(+) and CD8(+) T cells revealed the existence of TCR glycosylation differences between the two. Collectively, these results are consistent with the existence of conformational or topological lineage-specific differences in the TCR.CD3 from CD4(+) and CD8(+) wild type T cells. The differences may be relevant for cis interactions during antigen recognition and signal transduction.

TCR dynamics in human mature T lymphocytes lacking CD3 gamma

The contribution of CD3gamma to the surface expression, internalization, and intracellular trafficking of the TCR/CD3 complex (TCR) has not been completely defined. However, CD3gamma is believed to be crucial for constitutive as well as for phorbol ester-induced internalization. We have explored TCR dynamics in resting and stimulated mature T lymphocytes derived from two unrelated human congenital CD3gamma-deficient (gamma(-)) individuals. In contrast to gamma(-) mutants of the human T cell line Jurkat, which were selected for their lack of membrane TCR and are therefore constitutively surface TCR negative, these natural gamma(-) T cells constitutively expressed surface TCR, mainly through biosynthesis of new chains other than CD3gamma. However, surface (but not intracellular) TCR expression in these cells was less than wild-type cells, and normal surface expression was clearly CD3gamma-dependent, as it was restored by retroviral transduction of CD3gamma. The reduced surface TCR expression was likely caused by an impaired assembly or membrane transport step during recycling, whereas constitutive internalization and degradation were apparently normal. Ab binding to the mutant TCR, but not phorbol ester treatment, caused its down-modulation from the cell surface, albeit at a slower rate than in normal controls. Kinetic confocal analysis indicated that early ligand-induced endocytosis was impaired. After its complete down-modulation, TCR re-expression was also delayed. The results suggest that CD3gamma contributes to, but is not absolutely required for, the regulation of TCR trafficking in resting and Ag-stimulated mature T lymphocytes. The results also indicate that TCR internalization is regulated differently in each case.

Contribution of CD3 gamma to TCR regulation and signaling in human mature T lymphocytes

CD3 proteins may have redundant as well as specific contributions to the intracellular propagation and final effector responses of TCR-mediated signals at different checkpoints during T cell differentiation. We report here on the participation of CD3 gamma in the activation and effector function of human mature T lymphocytes at the antigen recognition checkpoint. Following TCR-CD3 engagement of human CD3 gamma-deficient T cell lines, and despite their lower TCR-CD3 surface levels compared to normal controls, mature T cell responses such as protein tyrosine phosphorylation and the regulation of expression of several cell surface molecules, including the TCR-CD3 itself, were either normal or only slightly affected. In contrast, other physiological responses like the specific adhesion and concomitant cell polarization on ICAM-1-coated dishes were selectively defective, and activation-induced cell death was increased. Our data indicate that CD3 gamma contributes essential specialized signaling functions to certain mature T cell responses. Failure to generate appropriate interactions may abort cytoskeleton reorganization and initiate an apoptotic response.

Conformational and biochemical differences in the TCR.CD3 complex of CD8(+) versus CD4(+) mature lymphocytes revealed in the absence of CD3gamma

Mature CD4(+) and CD8(+) T lymphocytes are believed to build and express essentially identical surface alphabeta T-cell receptor-CD3 (TCR.CD3) complexes. However, TCR.CD3 expression has been shown to be more impaired in CD8(+) cells than in CD4(+) cells when CD3gamma is absent in humans or mice. We have addressed this paradox by performing a detailed phenotypical and biochemical analysis of the TCR.CD3 complex in human CD3gamma-deficient CD8(+) and CD4(+) T cells. The results indicated that the membrane TCR.CD3 complex of CD8(+) T lymphocytes was conformationally different from that of CD4(+) lymphocytes in the absence of CD3gamma. In addition, CD8(+), but not CD4(+), CD3gamma-deficient T lymphocytes were shown to contain abnormally glycosylated TCRbeta proteins, together with a smaller, abnormal TCR chain (probably incompletely processed TCRalpha). These results suggest the existence of hitherto unrecognized biochemical differences between mature CD4(+) and CD8(+) T lymphocytes in the intracellular control of alphabetaTCR. CD3 assembly, maturation, or transport that are revealed when CD3gamma is absent. Such lineage-specific differences may be important in receptor-coreceptor interactions during antigen recognition.