Helper T-cell subsets: phenotype, function and the role of lymphokines in regulating their development

We have concentrated here on the lymphokines which might serve to regulate the different pathways of precursor development. We suggest that, as a result of antigenic stimulation, specific precursor cells both proliferate and become committed to develop into either an effector cell, a memory cell or an anergized cell. Anergy has not been dealt with in this review, but it is likely to be one of the options available. The development of an effector population takes 4-7 d (quite analogous to the time it takes for CTLp to become CTL and for resting B to become Ab-forming cells). The effector populations are large, generally IL-2R-positive cells. These cells have upregulated many adhesion molecule systems [e.g., Pgp-1, LFA-1 and ICAM-1 (Swain unpublished)], but downregulated the Mel-14 homing receptor. Effectors are ready to respond to APC such as specific B cells with a rapid synthesis and secretion of lymphokines. The effector population is then quickly downregulated, both by the turn off of lymphokine synthesis/secretion and possibly by its own suicide. This kind of pattern makes teleological sense since the cells making such high titers of lymphokines could have many potent pleitropic effects. It also seems to be the strategy employed in the generation of other terminally differentiated effectors (such as CTL and plasma cells). The requirement for restimulation and the requirement for direct and perhaps prolonged contact between the helper effector and the APC-B cell can be expected to help ensure that these lymphokines are localized (reviewed in Swain & Dutton 1987, Swain & Croft 1990) and effectively delivered to specific responding cells. We postulate that at the same time, or perhaps subsequent to this, another set of signals drives precursors to generate prememory cells. Our studies suggest these emerging memory cells may be phenotypically unique and we postulate that they are specialized to become a "long-lived" population of memory cells that will persist indefinitely as a protective population of increased frequency for the antigen encountered and which is also able to respond more rapidly and effectively. The greater effectiveness of the memory response would thus be due to dramatically increased frequency, to characteristic and stable changes in adhesion molecule expression and to the fact that, in addition to IL-2, resting memory cells also secrete at least low titers of IL-3, IL-4, IFN-gamma and other lymphokines upon initial restimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Laser speckle contrast imaging: theoretical and practical limitations

When laser light illuminates a diffuse object, it produces a random interference effect known as a speckle pattern. If there is movement in the object, the speckles fluctuate in intensity. These fluctuations can provide information about the movement. A simple way of accessing this information is to image the speckle pattern with an exposure time longer than the shortest speckle fluctuation time scale-the fluctuations cause a blurring of the speckle, leading to a reduction in the local speckle contrast. Thus, velocity distributions are coded as speckle contrast variations. The same information can be obtained by using the Doppler effect, but producing a two-dimensional Doppler map requires either scanning of the laser beam or imaging with a high-speed camera: laser speckle contrast imaging (LSCI) avoids the need to scan and can be performed with a normal CCD- or CMOS-camera. LSCI is used primarily to map flow systems, especially blood flow. The development of LSCI is reviewed and its limitations and problems are investigated.

Response of naive antigen-specific CD4+ T cells in vitro: characteristics and antigen-presenting cell requirements

Because of the low frequency of T cells for any particular soluble protein antigen in unprimed animals, the requirements for naive T cell responses in specific antigens have not been clearly delineated and they have been difficult to study in vitro. We have taken advantage of mice transgenic for the V beta 3/V alpha 11 T cell receptor (TCR), which can recognize a peptide of cytochrome c presented by IEk. 85-90% of CD4+ T cells in these mice express the transgenic TCR, and we show that almost all such V beta 3/V alpha 11 receptor-positive cells have a phenotype characteristic of naive T cells, including expression of high levels of CD45RB, high levels of L-selectin (Mel-14), low levels of CD44 (Pgp-1), and secretion of interleukin 2 (IL-2) as the major cytokine. Naive T cells, separated on the basis of CD45RB high expression, gave vigorous responses (proliferation and IL-2 secretion) to peptide antigen presented in vitro by a mixed antigen-presenting cell population. At least 50% of the T cell population appeared to respond, as assessed by blast transformation, entry into G1, and expression of increased levels of CD44 by 24 h. Significant contributions to the response by contaminating memory CD4+ cells were ruled out by demonstrating that the majority of the CD45RB low, L- selectin low, CD44 high cells did not express the V beta 3/V alpha 11 TCR and responded poorly to antigen. We find that proliferation and IL- 2 secretion of the naive CD4 cells is minimal when resting B cells present peptide antigen, and that both splenic and bone marrow-derived macrophages are weak stimulators. Naive T cells did respond well to high numbers of activated B cells. However, dendritic cells were the most potent stimulators of proliferation and IL-2 secretion at low cell numbers, and were far superior inducers of IL-2 at higher numbers. These studies establish that naive CD4 T cells can respond vigorously to soluble antigen and indicate that maximal stimulation can be achieved by presentation of antigen on dendritic cells. This model should prove very useful in further investigations of activation requirements and functional characteristics of naive helper T cells.

Sunlight exposure and risk of lens opacities in a population-based study: the Salisbury Eye Evaluation project

CONTEXT

Exposure to UV-B radiation in sunlight has been shown to increase the risk of cataract formation in high-risk occupational groups, but risk to the population has not been quantified.

OBJECTIVES

To determine the ocular exposure to UV-B radiation in sunlight for a population of older persons and to determine the association between UV-B and lens opacities.

DESIGN

The Salisbury Eye Evaluation project, a population-based cohort of older adults.

SETTING

Salisbury, Md.

PARTICIPANTS

A total of 2520 community-dwelling 65-year-old to 84-year-old adults in Salisbury, Md, from 1993 to 1995, of whom 26.4% were African Americans.

MAIN OUTCOME MEASURE

Association of photographically documented cortical opacity 3/16 or greater in at least 1 eye with ocular UV-B exposure, reported in Maryland sun-years of exposure.

RESULTS

The odds of cortical opacity increased with increasing ocular exposure to UV-B (odds ratio [OR], 1.10; 95% confidence interval [CI], 1.02-1.20). The relationship was similar for women (OR, 1.14; 95% CI, 1.00-1.30) and for African Americans (OR, 1.18; 95% CI, 1.04-1.33). Analyses of the ocular dose by each age group after the age of 30 years showed no vulnerable age group, suggesting damage is based on cumulative exposure.

CONCLUSIONS

Although this population of older Americans has relatively low ocular exposure to UV-B in sunlight, there is still an association between ocular exposure and increasing odds of cortical opacity. Our study found an association among African Americans, which, to our knowledge, has not been reported previously. All sex and racial groups would benefit from simple methods to avoid ocular sun exposure.

Detrimental effects of speckle-pixel size matching in laser speckle contrast imaging

Through a series of simulations and experiments, we demonstrate that the frequently cited criterion of matching speckle size to detector element (pixel) size in laser speckle contrast imaging (LSCI) has the detrimental effect of reducing the contrast and thereby decreasing the variation in the laser speckle contrast image. Unlike quasi-elastic light scattering, where this matching condition has been shown to maximize the signal-to-noise ratio, in LSCI, the minimum speckle size must exceed the Nyquist criterion in order to maximize the contrast of the speckle patterns.

Characterization of antigen-specific CD4+ effector T cells in vivo: immunization results in a transient population of MEL-14-, CD45RB- helper cells that secretes interleukin 2 (IL-2), IL-3, IL-4, and interferon gamma

In previous studies we demonstrated that, following activation by mitogens or alloantigens, helper T cell precursors proliferate and differentiate in vitro to produce a population of effector cells that secrete high titers of lymphokines upon restimulation. In this report, we demonstrate that a similar effector population develops in vivo following primary antigen stimulation. When restimulated with specific antigen in vitro, CD4+ T cells from mice primed 5 to 7 days previously by subcutaneous administration of keyhole limpet hemocyanin (KLH) in adjuvant, produced high levels of interleukin 2 (IL-2), IL-4, and IL-3, and little or no interferon gamma (IFN-gamma) or IL-5. The effector T cells provided excellent helper activity for in vitro antibody responses of 4-hydroxy-5-iodo-nitrophenyl acetic acid-primed B cells with the production principally of the immunoglobulin G1 (IgG1) and IgM isotypes, small quantities of IgG3, and no detectable IgG2a, or IgG2b. Antigen-specific secretion of IL-2, IL-3, and IL-4 by in vivo effectors was detectable by 12 hours following in vitro restimulation. IFN-gamma and IL-5 were not detected until 48 and 72 hours of culture, respectively, and low levels of these lymphokines were produced. Lymphokine production by primed CD4+ T cells could be induced as early as 3 days following immunization, peaked on day 5, and declined thereafter. The kinetics of in vivo appearance of effector CD4+ T cells that produce lymphokines upon restimulation in vitro were similar for each of the lymphokines examined. Mice depleted of precursor CD4+ T cells by adult thymectomy exhibited limited capacity to generate lymphokine secreting CD4+ T cells in response to primary immunization with KLH, suggesting that the majority of lymphokine producing T cells arise from short-lived and/or precursor cells. Separation of CD4+ T cells from KLH-primed mice on the basis of expression of the lymph node-specific homing receptor, MEL-14, revealed that antigen-specific production of IL-2, IL-3, IL-4, and IFN-gamma was exclusively associated with the MEL-14- subset of CD4+ T cells. Separation on the basis of CD45RB expression, demonstrated that antigen-specific lymphokine production was primarily associated with the minor CD45RB- population, which has been previously associated with memory activity. Our results indicate that primary in vivo immunization leads to the development of a transient population of helper-effectors with a unique phenotype that can produce large quantities of lymphokines and mediate excellent helper activity for B cells.(ABSTRACT TRUNCATED AT 400 WORDS)

A transcriptional silencer controls the developmental expression of the CD4 gene

The appropriate expression of the CD4 glycoprotein is required for T-cell function and development. Here we define the transcriptional control elements in the CD4 locus that convey CD(4+)-specific expression of a marker gene in transgenic mice. Using nuclear run-on experiments, we have determined that the major mechanism for CD4 expression control during development is transcriptional. We have identified a developmental stage- and tissue-specific negative regulatory element in the first intron of the murine CD4 gene that has the characteristics of a transcriptional silencer. The CD4 silencer functions to inhibit marker gene expression at two different stages of T-cell development, as well as in non-T hematopoietic cells, and thus is the critical controlling element responsible for T-cell-specific, as well as developmental- and subclass-specific, expression.

Can laser speckle flowmetry be made a quantitative tool?

The ultimate objective of laser speckle flowmetry (and a host of specific implementations such as laser speckle contrast analysis, LASCA or LSCA; laser speckle spatial contrast analysis, LSSCA; laser speckle temporal contrast analysis, LSTCA; etc.) is to infer flow velocity from the observed speckle contrast. Despite numerous demonstrations over the past 25 years of such a qualitative relationship, no convincing quantitative relationship has been proven. One reason is a persistent mathematical error that has been propagated by a host of workers; another is a misconception about the proper autocorrelation function for ordered flow. Still another hindrance has been uncertainty in the specific relationship between decorrelation time and local flow velocity. Herein we attempt to dispel some of these errors and misconceptions with the intent of turning laser speckle flowmetry into a quantitative tool. Specifically we review the underlying theory, explore the impact of various analytic models for relating measured intensity fluctuations to scatterer motion, and address some of the practical issues associated with the measurement and subsequent data processing.

Structure of the Shigella dysenteriae haem transport locus and its phylogenetic distribution in enteric bacteria

The ability to transport and use haemin as an iron source is frequently observed in clinical isolates of Shigella spp. and pathogenic Escherichia coli. We found that many of these haem-utilizing E. coli strains contain a gene that hybridizes at high stringency to the S. dysenteriae type 1 haem receptor gene, shuA. These shuA-positive strains belong to multiple phylogenetic groups and include clinical isolates from enteric, urinary tract and systemic infections. The distribution of shuA in these strains suggests horizontal transfer of the haem transport locus. Some haem-utilizing pathogenic E. coli strains did not hybridize with shuA, so at least one other haem transport system is present in this group. We also characterized the chromosomal region containing shuA in S. dysenteriae. The shuA gene is present in a discrete locus, designated the haem transport locus, containing eight open reading frames. Several of the proteins encoded in this locus participate with ShuA in haem transport, as a Salmonella typhimurium strain containing the entire haem transport locus used haem much more efficiently than the same strain containing only shuA. The haem transport locus is not present in E. coli K-12 strains, but the sequences flanking the haem transport locus in S. dysenteriae matched those at the 78.7 minute region of E. coli K-12. The junctions and flanking sequences in the shuA-positive pathogenic E. coli strains tested were nearly identical to those in S. dysenteriae, indicating that, in these strains, the haem transport locus has an organization similar to that in S. dysenteriae, and it is located in the same relative position on the chromosome.

Influence of ethanol consumption on natural killer cell activity in mice

Alcohol is a known suppressant to the immune system, and alcoholics frequently have impaired humoral and cell-mediated immunity. Several studies indicate that alcohol modulates natural killer (NK) cell activity. NK cells provide important defense against certain infectious diseases, spontaneously arising tumors and, in particular, to blood-borne metastasizing tumor cells. Evaluation of the effects of alcohol on NK cells is complicated by many factors including: the level and duration of alcohol abuse, polydrug use, the subject's age, and nutritional and health status. This study examined the effects of 1 and 2 weeks of alcohol consumption on baseline and interleukin 2 (IL-2) stimulated murine NK cell activity. Well nourished female C57BL/6 mice were given continuous access to 20% w/v ethanol as the sole fluid source and consumed about 40% of their total caloric intake as ethanol. Splenic baseline and IL-2 stimulated NK cell activity were significantly lower in ethanol-consuming groups compared to control groups after the 1- and 2-week test periods. The average daily intake of ethanol, blood alcohol concentration, and the percentage of ethanol-derived calories were not associated with the decreased NK cell activity of the experimental animals; nor did any other measured parameter appear to serve as an indicator of ethanol modulation of splenic NK cell activity. Whether this immunosuppression results from the "direct" modulation of ethanol or from indirect factors is presently unknown.

A computerized diet history questionnaire for epidemiologic studies

OBJECTIVE

To describe methods used to computerize the diet history questionnaire developed for the Coronary Artery Risk Factor Development in Young Adult (CARDIA) study and to describe quality-control procedures used in conjunction with dietary assessment.

DESIGN

The computerized diet history is being used in a case-control study. Because of the computerized nature of the questionnaire, we developed quality-control procedures that incorporate listening to an audiotape of the interview while visually reviewing recorded data.

SETTING

Three centers involved in a population-based epidemiologic study of colon cancer.

SUBJECTS

Men and women between the ages of 30 and 79 years.

RESULTS

Quality-control results showed that 100% of the computerized forms would be free of errors if the data were subjected to visual review only. Probing errors, which accounted for 47.3% of all errors, were the most commonly encountered errors. In probing errors the interviewer did not probe in a nondirective manner, or the interviewer failed to verify responses that might be considered questionable.

APPLICATIONS

The CARDIA diet history was computerized for use in epidemiologic studies of the association between diet and disease. Review of the audiotapes of the interviews showed that most errors made in obtaining a dietary assessment were not detectable from visual review of the data. Although the quality-control procedures were developed for a computerized diet history questionnaire, they are applicable to other dietary assessment methods.

The spineless-aristapedia and tango bHLH-PAS proteins interact to control antennal and tarsal development in Drosophila

The Drosophila spineless (ss) gene encodes a basic-helix-loop-helix-PAS transcription factor that is required for proper specification of distal antennal identity, establishment of the tarsal regions of the legs, and normal bristle growth. ss is the closest known homolog of the mammalian aryl hydrocarbon receptor (Ahr), also known as the dioxin receptor. Dioxin and other aryl hydrocarbons bind to the PAS domain of Ahr, causing Ahr to translocate to the nucleus, where it dimerizes with another bHLH-PAS protein, the aryl hydrocarbon receptor nuclear translocator (Arnt). Ahr:Arnt heterodimers then activate transcription of target genes that encode enzymes involved in metabolizing aryl hydrocarbons. In this report, we present evidence that Ss functions as a heterodimer with the Drosophila ortholog of Arnt, Tango (Tgo). We show that the ss and tgo genes have a close functional relationship: loss-of-function alleles of tgo were recovered as dominant enhancers of a ss mutation, and tgo-mutant somatic clones show antennal, leg, and bristle defects almost identical to those caused by ss(−) mutations. The results of yeast two-hybrid assays indicate that the Ss and Tgo proteins interact directly, presumably by forming heterodimers. Coexpression of Ss and Tgo in Drosophila SL2 cells causes transcriptional activation of reporters containing mammalian Ahr:Arnt response elements, indicating that Ss:Tgo heterodimers are very similar to Ahr:Arnt heterodimers in DNA-binding specificity and transcriptional activation ability. During embryogenesis, Tgo is localized to the nucleus at sites of ss expression. This localization is lost in a ss null mutant, suggesting that Tgo requires heterodimerization for translocation to the nucleus. Ectopic expression of ss causes coincident ectopic nuclear localization of Tgo, independent of cell type or developmental stage. This suggests that the interaction of Ss and Tgo does not require additional signals, unlike the ligand-dependent interaction of Ahr and Arnt. Despite the very different biological roles of Ahr and Arnt in insects and mammals, the molecular mechanisms by which these proteins function appear to be largely conserved.

Transvection in the iab-5,6,7 region of the bithorax complex of Drosophila: homology independent interactions in trans

The Abdominal-B (Abd-B) gene of the bithorax complex (BX-C) of Drosophila controls the identities of the fifth through seventh abdominal segments and segments in the genitalia (more precisely, parasegments 10-14). Here we focus on iab-5, iab-6 and iab-7, regulatory regions of Abd-B that control expression in the fifth, sixth and seventh abdominal segments (parasegments 10-12). By analysis of partial BX-C deficiencies, we show that these regions are able to promote fifth and sixth abdominal segment identities in the absence of an Abd-B gene in cis. We establish that this ability does not result from cis-regulation of the adjacent abd-A or Ubx genes of the BX-C but rather occurs because the iab-5,6,7 region is able to interact with Abd-B in trans. We demonstrate that this interaction is proximity dependent and is, therefore, a case of what E. B. Lewis has called transvection. Interactions of this type are presumably facilitated by the synapsis of homologues that occurs in somatic cells of Dipterans. Although transvection has been detected in a number of Drosophila genes, transvection of the iab-5,6,7 region is exceptional in two ways. First, interaction in trans with Abd-B does not require that homologues share homologous sequences within, or for some distance to either side of, the BX-C. This is the first case of transvection shown to be independent of local synapsis. A second unusual feature of iab-5,6,7 transvection is that it is remarkably difficult to disrupt by heterozygosity for chromosome rearrangements. The lack of requirement for local synapsis and the tenacity of trans-interaction argue that the iab-5,6,7 region can locate and interact with Abd-B over considerable distance. This is consistent with the normal role of iab-5,6,7, which must act over some 20-60 kb to influence its regulatory target in cis at the Abd-B promoter. Evidence is presented that trans-action of iab-5,6,7 requires, and may be mediated by, the region between distal iab-7 and Abd-B. Also, we show that iab-5,6,7 transvection is independent of the allelic state of zeste, a gene that influences several other cases of transvection. The long-range nature of interactions in trans between iab-5,6,7 and Abd-B suggests that similar interactions could operate effectively in organisms lacking extensive somatic pairing. Transvection may, therefore, be of more general significance than previously suspected.

Randomized controlled trial of a low animal protein, high fiber diet in the prevention of recurrent calcium oxalate kidney stones

Low protein diets are commonly prescribed for patients with idiopathic calcium nephrolithiasis, who account for > 80% of new diagnoses of kidney stones. This dietary advice is supported by metabolic studies and epidemiologic observational studies but has not been evaluated in a controlled trial. Using 1983-1985 data from three Northern California Kaiser Permanente Medical Centers, the authors randomly assigned 99 persons who had calcium oxalate stones for the first time to a low animal protein, high fiber diet that contained approximately 56-64 g daily of protein, 75 mg daily of purine (primarily from animal protein and legumes), one-fourth cup of wheat bran supplement, and fruits and vegetables. Intervention subjects were also instructed to drink six to eight glasses of liquid daily and to maintain adequate calcium intake from dairy products or calcium supplements. Control subjects were instructed only on fluid intake and adequate calcium intake. Both groups were followed regularly for up to 4.5 years with food frequency questionnaires, serum and urine chemistry analysis, and abdominal radiography; and they were urged to comply with dietary instructions. In the intervention group of 50 subjects, stones recurred in 12 (7.1 per 100 person-years) compared with two (1.2 per 100 person-years) in the control group; both groups received a mean of 3.4 person-years of follow-up (p = 0.006). After adjustment for possible confounding effects of age, sex, education, and baseline protein and fluid intake, the relative risk of a recurrent stone in the intervention group was 5.6 (95% confidence interval 1.2-26.1) compared with the control group. The authors conclude that advice to follow a low animal protein, high fiber, high fluid diet has no advantage over advice to increase fluid intake alone.

Statistics of local speckle contrast

In describing the first-order properties of laser speckle under polarized illumination conditions, it is almost an article of faith that the contrast is unity. In many processing schemes, however, the contrast defined as the quotient of the standard deviation and the mean is calculated over a localized spatial region. In such cases, this local contrast displays a distribution of values that can depart substantially from unity. Properties of this distribution depend on details of the data acquisition and on the size of the local neighborhood over which the contrast is calculated. We demonstrate that this local contrast can be characterized in terms of a log-normal distribution. Further, we show that the two defining parameters of this model can in turn be expressed in terms of the minimum speckle size and the extent of the local neighborhood. Performance of the model is illustrated with some typical optical coherence tomography data.

OCT-based elastography for large and small deformations

We present two approaches to speckle tracking for optical coherence tomography (OCT)-based elastography, one appropriate for small speckle motions and the other for large, rapid speckle motions. Both approaches have certain advantages over traditional cross-correlation based motion algorithms. We apply our algorithms to quantifying the strain response of a mechanically inhomogeneous, bi-layered polyvinyl alcohol tissue phantom that is subjected to either small or large dynamic compressive forces while being imaged with a spectral domain OCT system. In both the small and large deformation scenarios, the algorithms performed well, clearly identifying the two mechanically disparate regions of the phantom. The stiffness ratio between the two regions was estimated to be the same for the two scenarios and both estimates agreed with the expected stiffness ratio based on earlier mechanical testing. No single numerical approach is appropriate for all cases and the experimental conditions dictate the proper choice of speckle shift algorithm for OCT-based elastography studies.

Effects of water immersion to the neck on pulmonary circulation and tissue volume in man

Utilizing the rebreathing of a gas mixture containing C2H2, C180, He O2, and N2, we obtained serial measurements of the pulmonary capillary blood flow (Qc), diffusing capacity per unit of alveolar volume (DL/VA), functional residual capacity (FRC), pulmonary tissue plus capillary blood volume (VTPC), and O2 comsumption (VO2) in five normal subjects under the following conditions: 1) 6 h of sitting, 2) 4 h of sitting while immersed in thermoneutral water to the neck, and 3) 4 h of lying in thermoneutral water to the neck. Water immersion (NI) was preceded and followed by 1-h prestudy and 1-h recovery periods. The measurements were made at 30-min intervals. Seated NI produced a fourfold increase in sodium excretion (UNaV), a 25-36% increase in Qc, a 45-59% increase in DL/VA, and a 30-36% decrease in FRC. This occurred as early as the 1st h of NI and persisted throughout the 4-h period of study. Throughout the seated control and NI periods, VO2, heart rate, and VTPC remained constant. During supine NI, Qc, HR, DL/VA, FRC, and VO2 did not differ significantly from supine prestudy. These date demonstrate that seated NI causes a significant increase of Qc and DL/VA which persists throughout the immersion period. Furthermore, the lack of change of VTPC suggests that the central vascular engorgement induced by seated NI is not accompanied by extravasation of fluid into the pulmonary interstitial space.

A survey of antimicrobial usage on dairy farms and waste milk feeding practices in England and Wales

The cause for the high prevalence of cefotaximase-producing Escherichia coli reported in dairy calves is unknown but may be partly due to the selective pressure of antimicrobial residues in waste milk (milk unfit for human consumption) fed to the calves. Antimicrobial use and waste milk feeding practices were investigated in 557 dairy farms in 2010/2011 that responded to a randomised stratified postal survey. The mean number of cases of mastitis per herd in the previous year was 47, and 93 per cent of respondents used antibiotic intra-mammary tubes to treat mastitis. The most frequently used lactating cow antibiotic tubes contained dihydrostreptomycin, neomycin, novobiocin, and procaine penicillin (37 per cent), and cefquinome (29 per cent). Ninety-six per cent of respondents used antibiotic tubes at the cessation of lactation ('drying off'). The most frequently used dry cow antibiotic tube (43 per cent) contained cefalonium. Frequently used injectable antibiotics included tylosin (27 per cent), dihydrostreptomycin and procaine penicillin (20 per cent) and ceftiofur (13 per cent). Eighty-three per cent of respondents (413) fed waste milk to calves. Of these 413, 87 per cent fed waste milk from cows with mastitis, and only one-third discarded the first milk after antibiotic treatment. This survey has shown that on more than 90 per cent of the farms that feed waste milk to calves, waste milk can contain milk from cows undergoing antibiotic treatment. On some farms, this includes treatment with third- and fourth-generation cephalosporins. Further work is underway to investigate the presence of these antimicrobials in waste milk.

Racial differences in lens opacities: the Salisbury Eye Evaluation (SEE) project

The purpose of this study was to determine racial differences in the prevalence of different types of lens opacities and cataract surgery. Between 1993 and 1995, the Salisbury Eye Evaluation (SEE) Project enrolled a representative sample of 2,520 community-dwelling persons aged 65-84 years in Salisbury, Maryland, 26.4% of whom were African-American. Participants received a full eye examination, and photographs were taken for documentation of lens status. Photographs were graded using a standardized grading system for the presence of cortical, nuclear, or posterior subcapsular cataract (PSC) opacification in at least one eye. The odds of having cortical opacities were 4.0 times greater among African Americans than among Caucasians (95% confidence interval (CI) 3.3-4.8). Caucasians were significantly more likely to have nuclear opacities (odds ratio = 2.1, 95% CI 1.7-2.6) and PSC opacities (odds ratio = 2.5, 95% CI 1.7-3.6). The odds of cataract surgery were 2.8 times higher among Caucasians, but these differences did not explain the differences in the prevalence of different types of lens opacities by racial group. With lower rates of nuclear and PSC opacities than Caucasians, African Americans may have a lower demand for cataract surgery. However, even with these differences, there is still significant unnecessary loss of vision due to cataract among older African Americans, for whom programs to ensure access to surgical care are indicated.

Visual and cognitive deficits predict stopping or restricting driving: the Salisbury Eye Evaluation Driving Study (SEEDS)

PURPOSE

To determine the visual and other factors that predict stopping or restricting driving in older drivers.

METHODS

A group of 1425 licensed drivers aged 67 to 87 years, who were residents of greater Salisbury, participated. At 1 year after enrollment, this group was categorized into those who had stopped driving, drove only within their neighborhood, or continued to drive beyond their neighborhood. At baseline, a battery of structured questionnaires, vision, and cognitive tests were administered. Multivariate analysis determined the factors predictive of stopping or restricting driving 12 months later.

RESULTS

Of the 1425 enrolled, 1237 (87%) were followed up at 1 year. Excluding those who were already limiting their driving at baseline (n = 35), 1.5% (18/1202) had stopped and 3.4% (41/1202) had restricted their driving. The women (odds ratio [OR], 4.01; 95% confidence interval [CI], 2.05-8.20) and those who prefer to be driven (OR, 3.91; 95% CI, 1.91-8.00) were more likely to stop or restrict driving. Depressive symptoms increased likelihood of restricting or stopping driving (OR, 1.08; 95% CI, 1.009-1.16 per point Geriatric Depression Scale). Slow visual scanning and psychomotor speed (Trail Making Test, Part A: OR, 1.02; 95% CI, 1.01-1.03), poor visuoconstructional skills (Beery-Buktenica Test of Visual Motor Integration: OR, 1.14; 95% CI, 1.05-1.25), and reduced contrast sensitivity (OR, 1.15; 95% CI, 1.03-1.28) predicted stopping or reducing driving. Visual field loss and visual attention were not associated. The effect of vision on changing driving behavior was partially mediated by cognition, depression, and baseline driving preferences.

CONCLUSIONS

In this cohort, contrast sensitivity and cognitive function were independently associated with incident cessation or restriction of driving space. These data suggest drivers with functional deficits make difficult decisions to restrict or stop driving.

Role of antigen-presenting cells in the polarized development of helper T cell subsets: evidence for differential cytokine production by Th0 cells in response to antigen presentation by B cells and macrophages

Immune challenges can elicit polarized responses skewed towards the development of T helper type 1 (Th1) or Th2 T cell subsets. To determine if distinct antigen-presenting cells (APC) populations might selectively influence Th subset development, we studied the role of two key APC populations, B cells and macrophages, in the differentiation of effector Th populations from naive precursor Th in vitro. Antigen (Ag)-specific, naive CD4+ T cells were enriched from a mouse strain, AND, bearing a transgenic alpha/beta T cell receptor (TCR) encoding reactivity with pigeon cytochrome c peptide 88-104. Peptide Ag was used throughout these studies so that differences in the uptake and processing by the two APC populations would not influence the results. Both APC populations, activated B cells and bone marrow-derived macrophages, supported the development of effector Th having the capacity to secrete high levels of cytokines when restimulated. Regardless of APC population present during effector development, exogenous interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) had dominant effects on Th subset development. Thus, with both APC populations, effector Th generated in the presence of IFN-gamma acquired a Th1-type cytokine profile, Th generated with IL-4 acquired a Th2-type cytokine profile, and Th generated without IFN-gamma or IL-4 acquired a Th0-type cytokine profile. B cells and macrophages also had equivalent APC function in the restimulation of Th1 and Th2-like effectors, since only minor differences in cytokine production were noted for these effector populations when restimulated with the two APC populations. However, in 8 of 19 experiments, the Th0-like effector population generated in the presence of IL-2 differentially responded to restimulation with B cells and macrophages, secreting significantly more IFN-gamma when restimulated with B cells, and significantly more IL-4 when restimulated with macrophages. We also found that Th effector populations recultured in IFN-gamma or IL-4 assumed a more Th1 or Th2-like phenotype, respectively, regardless of their initial cytokine profile. We conclude that through a subtle capacity to skew cytokine production by a Th0 subset, different APC may selectively influence Th subset development under conditions of prolonged or chronic stimulation in an autocrine fashion.

A Myc-associated zinc finger protein binding site is one of four important functional regions in the CD4 promoter

The CD4 promoter plays an important role in the developmental control of CD4 transcription. In this report, we show that the minimal CD4 promoter has four factor binding sites, each of which is required for full function. Using biochemical and mutagenesis analyses, we determined that multiple nuclear factors bind to these independent sites. We determined that an initiator-like sequence present at the cap site and an Ets consensus sequence are required for full promoter function. We also demonstrate that the Myc-associated zinc finger protein (MAZ) appears to be the predominant factor binding to one of these sites. This last site closely resembles the ME1a1 G3AG4AG3 motif previously shown to be a critical element in the P2 promoter of the c-myc gene. We therefore believe that the MAZ transcription factor is also likely to play an important role in the control of developmental expression of the CD4 gene.