Biomedical subjects

H C Santiago

Publications and source records attributed to H C Santiago.

11 recordsLinked to original sources

PubMed2001

Combined interleukin-12 and topical chemotherapy for established Leishmaniasis drastically reduces tissue parasitism and relapses in susceptible mice.

The efficacy of the association of paromomycin sulfate (PA) with recombinant (r) interleukin (IL)-12 was investigated by topical treatment of BALB/c mice infected with Leishmania major that displayed fully developed cutaneous lesions. Although healing was observed in PA-treated groups, lesions recurred in 100% of these animals 70 days after treatment. In contrast, lesions were absent in a high proportion of PA- and rIL-12-treated mice 120 days after treatment. The PA/rIL-12-treated mice had a switch in cytokine response, from high IL-4 and low interferon (IFN)-gamma levels to low IL-4 and high IFN-gamma levels, and reductions in parasite load, dissemination of parasites, and inflammation. Thus, the association of rIL-12 to topical chemotherapy for leishmaniasis may be an important strategy for increasing cure rates and decreasing the incidence of relapse.

Administration, Cutaneous↗

PubMed2001

Prevalence of CD8(+)alpha beta T cells in Trypanosoma cruzi-elicited myocarditis is associated with acquisition of CD62L(Low)LFA-1(High)VLA-4(High) activation phenotype and expression of IFN-gamma-inducible adhesion and chemoattractant molecules.

The determinants of the prevalence of CD8(+) T cells in the inflamed myocardium of Trypanosoma cruzi-infected patients and experimental animals are undefined. Using C3H/He mice infected with the Colombiana strain of T. cruzi, we found that the distribution of CD4(+)/CD8(-) and CD4(-)/CD8(+) T cells in the myocardium mirrors the frequency of cells expressing the CD62L(Low)LFA-1(High)VLA-4(High) activation phenotype among CD4(+)/CD8(-) and CD4(-)/CD8(+ )peripheral blood T cells. Consistently, vascular cell adhesion molecule-1-positive endothelial cells and a fine fibronectin network surrounding VLA-4(+) mononuclear cells were found in the inflamed myocardium. Further, interferon gamma (IFN-gamma) and IFN-gamma-induced chemokines (RANTES, MIG and CRG-2/IP-10), as well as JE/MCP-1 and MIP1-alpha, were found to be the dominant cytokines expressed in situ during acute and chronic myocarditis elicited by T. cruzi. In contrast, interleukin 4 mRNA was only detected during the chronic phase. Altogether, the results indicate that the distribution of T-cell subsets in the myocardium of T. cruzi-infected mice reflects the particular profile of adhesion molecules acquired by most peripheral CD8(+) T lymphocytes and point to the possibility that multiple IFN-gamma-inducible molecules present in the inflamed tissue contribute to the establishment and maintenance of T. cruzi-induced myocarditis.

Animals↗

PubMed2000

Leishmania sp: comparative study with Toxoplasma gondii and Trypanosoma cruzi in their ability to initialize IL-12 and IFN-gamma synthesis.

We compared in vitro and in vivo induction of IL-12 (p40) and IFN-gamma by mouse cells stimulated with Toxoplasma gondii, Trypanosoma cruzi, and different species of Leishmania. Spleen cells cultured in vitro with T. cruzi or T. gondii, but not with Leishmania, produced IL-12 (p40) and IFN-gamma. Accordingly, IL-12 (p40) was produced by macrophages stimulated in vitro with live T. cruzi or T. gondii or membrane glycoconjugates obtained from trypomastigotes or tachyzoites. No IL-12 production was detected when macrophages were stimulated with live parasites or glycoconjugates from Leishmania, regardless of priming with IFN-gamma. In vivo, only T. cruzi and T. gondii induced the synthesis of IL-12 and IFN-gamma by mouse spleen cells after intraperitoneal injection of parasites. When injected subcutaneously, live Leishmania sp. induced IL-12 (p40) and IFN-gamma production by draining lymph node cells, albeit the levels were slightly lower than those induced by infection with T. gondii or T. cruzi using the same route. Together our results indicate that under different conditions, the intracellular protozoa T. gondii and T. cruzi are more potent stimulators of IL-12 and IFN-gamma synthesis by host immune cells than parasites of the genus Leishmania.

Animals↗

PubMed1999

Coinfection with Toxoplasma gondii inhibits antigen-specific Th2 immune responses, tissue inflammation, and parasitism in BALB/c mice infected with Leishmania major.

Lesion size, cellular infiltration, and tissue parasitism in the footpads of BALB/c mice infected with Leishmania major were all dramatically inhibited during acute but not chronic infection with Toxoplasma gondii. Similarly, acute but not chronic toxoplasmosis at the time of infection with L. major had a strong inhibitory effect on development of acquired immune responses mediated by Th2 lymphocytes. In contrast, no major changes in Leishmania-specific Th1-mediated responses were observed in mice coinfected with T. gondii.

Animals↗

PubMed1998

Induction of cell-mediated immunity during early stages of infection with intracellular protozoa.

Toxoplasma gondii and Trypanosoma cruzi are intracellular parasites which, as part of their life cycle, induce a potent cell-mediated immunity (CMI) maintained by Th1 lymphocytes and IFN-gamma. In both cases, induction of a strong CMI is thought to protect the host against rapid parasite multiplication and consequent pathology and lethality during the acute phase of infection. However, the parasitic infection is not eliminated by the immune system and the vertebrate host serve as a parasite reservoir. In contrast, Leishmania sp, which is a slow growing parasite, appears to evade induction of CMI during early stages of infection as a strategy for surviving in a hostile environment (i.e., inside the macrophages which are their obligatory niche in the vertebrate host). Recent reports show that the initiation of IL-12 synthesis by macrophages during these parasitic infections is a key event in regulating CMI and disease outcome. The studies reviewed here indicate that activation/inhibition of distinct signaling pathways and certain macrophage functions by intracellular protozoa are important events in inducing/modulating the immune response of their vertebrate hosts, allowing parasite and host survival and therefore maintaining parasite life cycles.

Animals↗

PubMed1994

Visual recognition memory in specific learning-disabled children.

BACKGROUND: Reading depends on the efficient storage and retrieval of visual and verbal information. Some studies have shown deficits of specific learning-disabled children in the recall and recognition of visual stimuli. This deficit is usually interpreted to be secondary to a verbal labelling deficiency. In this experiment, we presented serial lists of complex geometric stimuli to a group of specific learning-disabled children (LD) and a non-disabled control group (NLD) at both the elementary and secondary school levels. We hypothesized that the NLD visual recognition performance would be superior to that of the LD group at the elementary school level, but not at the secondary school level. We further hypothesized that the difference was related to inefficient primary visual rehearsal strategies. METHODS: 20 elementary school children (11 LD and 9 NLD) and 31 secondary school children (15 LD and 16 NLD) were presented serial lists of four geometric figures. A probe was presented after a 1 second delay. The subjects pressed a key if the probe was in the list ("same" response) or another key if the probe was not in the list ("different" response). Type of response (correct or incorrect) and reaction time was measured at each serial position for "same" and "different" responses. RESULTS: At the elementary school level, there was a significant visual recognition memory advantage of the NLD group over the LD group (F(1,8) = 6.83, p = 0.018), but there was no significant difference between these groups at the secondary school level. There was no significant difference in the reaction time between the groups at either of the two levels. CONCLUSIONS: LD children have poorer visual recognition memory performance than NLD children for complex geometric patterns. Since there was no difference in reaction time between the two groups, attentional or encoding deficits can not adequately explain the recognition memory differences. The results can best be explained by inefficient visual rehearsal strategies with a small pool of visual items that are unfamiliar and difficult to code verbally. The serial recognition task can be used effectively by the optometrist to discriminate the performance of LD and NLD children.

Child↗

PubMed1992

The recruitment and retention of disadvantaged and underrepresented groups in optometry.

The recruitment and retention of disadvantaged students represents a formidable challenge to optometric educators. Referrals by optometrists and counsellors, visits to minority campuses, and information through the news media can help the recruitment process. Academic achievement and retention rates can be enhanced by tutorial programs, development of learning centers, learning modules, self-paced materials, and computer software. The most important element is the sensitivity of faculty and administrators to the educational needs of the students and the health care needs of disenfranchised populations.

Humans↗

PubMed1985

Memory processing of serial lists by pigeons, monkeys, and people.

List memory of pigeons, monkeys, and humans was tested with lists of four visual items (travel slides for animals and kaleidoscope patterns for humans). Retention interval increases for list-item memory revealed a consistent modification of the serial-position function shape: a monotonically increasing function at the shortest interval, a U-shaped function at intermediate intervals, and a monotonically decreasing function at the longest interval. The time course of these changes was fastest for pigeons, intermediate for monkeys, and slowest for humans.

Adult↗

PubMed1984

Pigeon memory: same/different concept learning, serial probe recognition acquisition, and probe delay effects on the serial-position function.

Two pigeons were trained with sets of 70 pairs of color-slide stimuli in a same/different task to perform at least 88% correct; six different sets were used in successive acquisitions. The subjects transferred same/different performance to novel stimuli with 60% accuracy following their six acquisitions; further training and daily changes in the training stimuli revealed 71% transfer to novel stimuli. Four pigeons were trained (88% criterion) in a serial-probe-recognition task with three list items, and the list length was increased with successive acquisitions to four, five, and six list items. Their serial-position functions changed for different delays between the last list item and the test item revealing a recency effect (last items remembered well) for 0-s delay, recency and primacy effects (first items remembered well) for 1- and 2-s delays, and only a primacy effect for a 10-s delay. These results are discussed in relation to human memory performance and theories of memory processing generally.

Animals↗

PubMed1984

Monkey memory: same/different concept learning, serial probe acquisition, and probe delay effects.

Three rhesus monkeys were trained and tested in a same/different task with six successive sets of 70 item pairs to an 88% accuracy on each set. Their poor initial transfer performance (55% correct) with novel stimuli improved dramatically to 85% correct following daily item changes in the training stimuli. They acquired a serial-probe-recognition (SPR) task with variable (1-6) item list lengths. This SPR acquisition, although gradual, was more rapid for the monkeys than for pigeons similarly trained. Testing with a fixed list length of four items at different delays between the last list item and the probe test item revealed changes in the serial-position function: a recency effect (last items remembered well) for 0-s delay, recency and primacy effects (first and last list items remembered well) for 1-, 2-, and 10-s delays, and only a primacy effect for the longest 30-s delay. These results are compared with similar ones from pigeons and are discussed in relation to theories of memory processing.

Animals↗

PubMed1980

Brightness contrast: a reinterpretation of compound cue and combined cue experiments with pigeons.

A group of three pigeons was trained on a 4-ply multiple schedule: a green color and a vertical line superimposed upon an achromatic background as positive stimuli, and a red color and a horizontal line on an achromatic background as negative stimuli. The pigeons were tested with the vertical line superimposed upon different achromatic background intensities, then with the vertical line superimposed upon different green background intensities, and finally with the vertical line and its training achromatic backgfound attenuated (and unattenuated) by a neutral density filter. The gradients peaked at the luminance of the achromatic background used during training and at the equivalent luminance for the green background when it was substituted for the achromatic background. The brightness contrast, not the background luminance, was the critical variable as the neutral density filter attenuated both the line and the background equally, leaving brightness contrast unchanged; there was no response decrement to this attenuated stimulus. Two other groups of three pigeons showed that they attended to line orientation as well as to brightness contrast. The brightness contrast hypothesis was extended to explain results of attention experiments and combined cue experiments which have used line stimuli in combinations with different backgrounds.

Animals↗