The effect of age on the antigen-presenting mechanism in limiting dilution precursor cell frequency analysis

We have utilized limiting dilution analysis (LDA)2 to compare the intrinsic precursor cytotoxic T lymphocyte (pCTL) frequency for influenza-plus-self in young and old C57BL/6 mice. Under conditions of excess interleukin 2 (IL-2) and antigen presenting cells (APC) derived from spleens of mice matched in age to those being tested, we found more than a twofold difference in pCTL frequency between young and old animals. However, there was no difference in pCTL frequency between the two age groups if antigen was presented to the old responder cells on spleen cells derived from young mice. The apparent decrease in pCTL frequency in old mice by standard LDA may in fact be due to a defect in the antigen processing and/or presentation mechanism of old spleen cells. We conclude that the age-associated defective CTL activity previously reported by us and by others may be due at least in part to a defect in the antigen presentation mechanism of aging mice.     

Pulmonary epithelial sieving of small solutes in rat lungs

Transport and consumption of glucose from the air spaces of isolated, fluid-filled lungs can result in significantly lower glucose concentrations in the air spaces than in the perfusate compartment (11). This concentration difference could promote the osmotic movement of water from the air spaces to the perfusate, but the rate of fluid extraction from the air spaces would then be limited by the rates of electrolyte transport through the epithelium. In the present study, measurements were made of solute and water losses from the air spaces of fluid-filled rat lungs and the transport of these solutes and water into the vasculature after addition of hypertonic glucose or sucrose to the perfusate. Increases in the concentrations of Na+, Cl-, K+, and labeled mannitol in the air space were initially comparable to those of albumin labeled with Evans blue. Similarly, decreases in electrolyte concentrations in the perfusate were comparable to those of labeled albumin, indicating that very little solute accompanied the movement of water out of the lungs. Nor was evidence found that exposure of the vasculature to hypertonic glucose resulted in an increase in the rate at which fluid was reabsorbed from the air spaces over a 1-h interval, aside from an initial, abrupt loss of solute-free water from the lungs. These observations suggest that perfusion of fluid-filled lungs with hypertonic solutions of small solutes results in the extraction of water from the air spaces and pulmonary parenchyma across membranes that resist the movement of electrolytes and other lipophobic solutes.     

Movement of ions and small solutes across endothelium and epithelium of perfused rabbit lungs

In situ and isolated fluid-filled rabbit lungs were used to study the transport of indicators between the air space and vascular compartments. These indicators were placed in either the perfusate or air spaces and samples were collected from the perfusate at intervals during a 1-h perfusion period. At the end of the hour, fluid was pumped out of the air space compartment into serial tubes and indicator concentrations were determined in both the air space and perfusion fluids. One hour after introducing the indicators into the air space, the relative decreases in solute concentration were (arranged from the greatest to the least decline): [14C]urea greater than 36Cl- = 125I- greater than 22Na+ greater than [3H]mannitol. The relative rates at which the indicators appeared in the perfusate were similar. When the indicators were placed in the perfusate, a similar relationship was observed in the increase in air space concentrations, but the loss of 22Na+ from the perfusate was similar to those of 36Cl- and 125I-. Losses of all indicators from the perfusate were two or more times those from the air spaces, and although the loss of [3H]mannitol from the perfusate was similar to that of 22Na+ for about 30 min, subsequent loss was much slower. Very little 125I-albumin traversed the tissue barrier, and the small changes in the concentrations of 125I-albumin in the air spaces suggested that little fluid movement had occurred. These studies suggest that the epithelium is less permeable to solutes than the endothelium and permits passage of anions at a faster rate than 22Na+.(ABSTRACT TRUNCATED AT 250 WORDS)     

A monoclonal antibody to viral glycoprotein blocks virus-immune effector T cells operating at H-2Dd but not at H-2Kd1.

A particular monoclonal antibody that binds to the influenza virus HA molecule inhibits HA-specific thymus-derived lymphocytes mediating cytotoxicity in the context of H-2Dd but not of H-2Kd. Another monoclonal antibody blocks both sets of HA-specific effector T cells. This observation, together with related findings from other laboratories, is considered to support the idea that T cell recognition is directed against some association of viral and H-2 glycoproteins, as proposed in the original formulation of the "altered self" concept.     

Characteristics of secondary cytotoxic T-cell responses in mice infected with influenza A viruses.

The cytotoxic T-cell response in mice infected with type A influenza viruses is dominated by a highly cross-reactive component. Previous experiments showed that after primary immunization the cytotoxic T-cell response apparently consists of a small but significant portion which is specific for the immunizing virus, and a larger component which is highly cross-reactive among all A strain viruses. The present study concentrates on the specificity of the T-cell response after secondary stimulation, using various combinations of type A virus strains. The underlying rationale was to determine whether there was any discernable pattern in the T-cell response which parallels the serologically defined antigenic pattern of influenza.That a virus strain-specific set of precursors does exist was evident in the primary response and even more so upon secondary challenge with the homologous virus (using an adoptive transfer protocol). However, upon secondary challenge with a heterologous influenza virus, this specific component was not evident no matter how closely related serologically the two challenge viruses were. No obvious relationships could be found between serologically defined antigenic patterns and the capacity to stimulate a secondary T-cell response specific for a particular type A influenza virus.     

Challenges for vaccination in the elderly

The increased susceptibility of the elderly to infection presents a major challenge to public health services. An aging immune system is well documented as the cause of increased infection rates in elderly people. Such immunosenescence is multi-factorial and incompletely understood. Immunosenescent changes include malfunctioning of innate immune system cellular receptors; involution of the thymus, with consequent reduction of the naïve T cell population; alteration of the T cell population composition; modified phenotypes of individual T cells; and replicative senescence of memory cells expressing naïve markers. Unfortunately, immunosenescence also renders vaccination less effective in the elderly. It is therefore important that the vaccines used against common but preventable diseases, such as influenza, are specifically enhanced to overcome the reduced immune responsiveness of this vulnerable population.     

Differential impairment of lytic and cytokine functions in senescent human immunodeficiency virus type 1-specific cytotoxic T lymphocytes

Telomere length is abnormally short in the CD8(+) T-cell compartment of human immunodeficiency virus type 1 (HIV-1)-infected persons, likely because of chronic cell turnover. Although clonal exhaustion of CD8(+) cytotoxic T lymphocytes (CTL) has been proposed as a mechanism for loss of antigen-specific responses, the functional consequences of exhaustion are poorly understood. Here we used telomerase transduction to evaluate the impact of senescence on CTL effector functions. Constitutive expression of telomerase in an HIV-1-specific CTL clone results in enhanced proliferative capacity, in agreement with prior studies of other human cell types. Whereas the CTL remain phenotypically normal in terms of antigenic specificity and requirements for proliferation, their cytolytic and antiviral capabilities are superior to those of control CTL. In contrast, their ability to produce gamma interferon and RANTES is essentially unchanged. The selective enhancement of cytolytic function in memory CTL by ectopic telomerase expression implies that loss of this function (but not cytokine production) is a specific consequence of replicative senescence. These data suggest a unifying mechanism for the in vivo observations that telomere lengths are shortened in the CD8(+) cells of HIV-1-infected persons and that HIV-1-specific CTL are deficient in perforin. Telomerase transduction could therefore be a tool with which to explore a potential therapeutic approach to an important pathophysiologic process of immune dysfunction in chronic viral infection.     

Stop-flow studies of solute uptake in rat lungs

Stop-flow studies were used to characterize solute uptake inisolated rat lungs. These lungs were perfused at 8 or 34 ml/min for10-28 s with solutions containing¹²⁵I-albumin and two or more ofthe following diffusible indicators: [³H]mannitol,[¹⁴C]urea,³HOH,²⁰¹Tl⁺,or⁸⁶Rb⁺.After this loading period, flow was stopped for 10-300 s and thenresumed to flush out the perfusate that remained in the pulmonary vasculature during the stop interval. Concentrations of²⁰¹Tl⁺and⁸⁶Rb⁺in the venous outflow decreased after the stop interval, indicating uptake from exchange vessels during the stop interval. The amount ofthese K⁺ analogs lost from thecirculation during the stop interval was greater when the intervalswere longer. However, losses of²⁰¹Tl⁺at 90 s approached those at 300 s. Because extraction continued afterthe vasculature had been flushed, vascular levels had presumably fallento negligible levels during the stop interval. By 90 s of stop flow thevascular volume that was cleared of²⁰¹Tl⁺averaged 0.657 ± 0.034 (SE) ml in the experiments perfused at 8 ml/min and 0.629 ± 0.108 ml in those perfused at 34 ml/min. Increases in perfusate K⁺decreased the cleared volumes of²⁰¹Tl⁺and⁸⁶Rb⁺.Uptake of[³H]mannitol,[¹⁴C]urea, and³HOH during the stop intervals wasobserved only when the lungs were loaded at high flow for shortintervals. Decreases in²⁰¹Tl⁺and⁸⁶Rb⁺concentrations in the pulmonary outflow can be used to identify thefraction of the collected samples that were within exchange vessels ofthe lung during the stop interval and may help determine thedistribution of solute and water exchange along the pulmonary vasculature.

     

Stop-flow studies of distribution of filtration in rat lungs

Lin, W., E. Jacobs, R. M. Schapira, K. Presberg, andR. M. Effros. Stop-flow studies of distribution offiltration in rat lungs. J. Appl.Physiol. 84(1): 47-52, 1998.The stop-flow approach was used to investigate where filtration occurs in the pulmonary vasculature after elevation of left atrial pressure andaspiration of HCl. Rat lungs were perfused for 11 min at zero leftatrial pressures, and then flow was stopped for 10 min and left atrialpressures were increased to 20 cmH₂O. Thereafter, ³HOH was instilled into the airspaces, and the pulmonary vasculature was flushed by perfusing it fromthe pulmonary artery to left atrium (anterograde flush) or in theopposite direction (retrograde flush). Increases in fluoresceinisothiocyanate (FITC)-dextran (molecular weight 2,000,000) indicatedfiltration, and these preceded increases in³HOH after anterograde but notretrograde flushes. This suggests that some filtration occurred throughvessels that were relatively venous compared with those through which³HOH exchange had occurred.Filtration increased fivefold after instillation of 0.1 N HCl inisotonic saline into the air spaces before perfusion. Increases inEvans blue-labeled albumin concentrations were <40% those ofFITC-dextran, indicating loss from the vasculature, but increases inunlabeled albumin and FITC-albumin were comparable.