Marathon runners (N = 22) who had completed at least seven marathons (X ± SEM = 23.6 ± 5.7) and had been training for marathon race events for at least 4 yr (12.3 ± 1.3) were compared with sedentary controls (N = 18). Although the two groups were of similar age (38.7 ± 1.5 and 43.9 ± 2.2 yr, respectively) and height, the marathon runners were significantly leaner and possessed a VO2max 60% higher than that of the controls. Neutrophil counts tended to be lower in the group of marathoners, while other leukocyte and lymphocyte subsets were similar to controls. Mitogen-induced lymphocyte proliferation did not differ between groups. Natural killer cell cyto-toxic activity (NKCA) was significantly higher in the marathoners versus controls (373 ± 38 vs 237 ± 41 total lytic units, respectively, a 57% difference, P = 0.02). For all subjects combined (N = 40) and within the group of marathon runners (N — 22), percent body fat was negatively correlated with NKCA (r = -0.48, P = 0.002; r = -0.49, P = 0.019, respectively), and age was negatively correlated with Con A-induccd lymphocyte proliferation (r = -0.41, P = 0.009; r = -0.53, P = 0.011, respectively). These data indicate that NKCA but not mitogen-induced lymphocyte proliferation is higher in marathon runners relative to sedentary controls.

Our previous report showed that the brain peptide Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) blocks the inhibitory effect of morphine sulfate on E-rosette formation by human peripheral blood lymphocytes (PBL). In this study, additional in vitro effects of Tyr-MIF-1 on human PBL were studied. The percentages of positive cells for CD 2, a sheep erythrocyte receptor, CD 4 and CD 8 were unchanged after incubation of PBL with morphine or morphine plus Tyr-MIF-1. Tyr-MIF-1 was not mitogenic by itself. The addition of Tyr-MIF-1 did not increase the proliferative response of PBL to Con A, although morphine did. Tyr-MIF-1 did not activate PBL to produce IL 2 nor did it affect the production of IL 2 by Con A-stimulated PBL. The results suggest that Tyr-MIF-1 does not directly modulate CD 2, CD 4 and CD 8 expression, does not alter the proliferative response of PBL, and does not affect the production of IL 2.

A exposição limitada ao Plasmodium chabaudi induz proeminente imunidade celular, associada à proteção de células T da apoptose. Este estudo tem como objetivo verificar a influência da carga parasitária na geração e manutenção dos linfócitos T e B de memória ao P. chabaudi. Assim, camundongos C57BL/6 foram submetidos à infecção tratada (subpatente) ou não (patente) com cloroquina após a inoculação de 106 eritrócitos parasitados (EP) e analisados nos dias 0, 20, 60, 120 e 200. Com relação à memória de linfócitos T, no dia 20, as freqüências de células CD4+ memória/ativadas e respondedoras aos EP foram significativamente maiores nos animais do grupo subpatente. Os níveis máximos de IgG2a específica foram encontrados no dia 120 em ambos os grupos. O desafio dos animais com 108 EP mostrou que a imunidade protetora declina progressivamente, mas os grupos ainda são capazes de estabelecer resposta secundária eficiente que elimine o parasita. Assim, podemos concluir que a carga parasitária influencia a fase aguda, mas não impede a geração e manutenção das células T e B de memória. / One of the main characteristics of malaria is the intense policlonal activation of splenic T and B lymphocytes induced by the parasite and the consequent elimination, through apoptosis, of part of these cells. However, the limited exposure to the bloodstage malaria seems to induce a prominent cellular immunity, associated with the protection of T lymphocytes from apoptosis. With this in mind, this study aimed to verify the influence of the parasite load in the generation and maintenance of memory T and B cells specific for Plasmodium chabaudi chabaudi AS. In order to evaluate this idea, C57BL/6 mice were infected with 106 parasitized red blood cells (pRBC) and submitted to a patent (untreated) or subpatent infection (controlled with sub-curative doses of chloroquine every time parasitemia reached 1%). Splenocytes from these mice were analyzed at 20, 60, 120 and 200 days after infection, regarding the pRBC-specific T cell proliferation and the expression of surface molecules, as CD4, CD8, CD62L, CD45RB, CD44, CD45R-B220 and IgG. The parasitemia and the splenocyte phenotype were also monitored after the challenge with 108 pRBC. Regarding T cell memory, at day 20 of infection, the frequencies of effector/activated CD4+ T cells (CD62LLOW CD45RBLOW/HIGH) were significantly increased in animals from the patent group, which was strict linked with the highest cellular activation observed in these animals. On the other hand, the total numbers of pRBCproliferating T (CD4+ and CD8+) cells per spleen were approximately 3-fold increased in subpatent animals, indicating that these cells were protected from apoptosis as a result of the limited exposure to the parasite. However, in both groups, these parameters decreased to values similar to those in controls at day 200. The splenocytes from both groups produced Th1 cytokines in response to pRBC in all times of analysis, but at the early phase of infection, Th2 cytokines were also observed, but without differences between the infected groups. Regarding memory B cells, the frequency of sIgG+ cells was increased at day 20 of infection, when 11% and 9% of CD45R+ cells from patent and subpatent animals were positive, respectively. For both groups, specific IgG2a antibodies attained maximum serum levels at day 120, but at day 200, it is possible to observe a significant decrease of these levels only in the serum of patent mice. Moreover, at day 200 of infection, mice of subpatent group showed significantly higher amounts of IgG2a that recognized the intra-erythrocytic forms of the parasite and the surface of infected erythrocytes. Challenge of mice with 108 pRBC showed that protective immunity progressively decline with time and despite the higher levels of specific antibody in subpatent mice, both groups showed similar protection. In experiments of adoptive transference to CD28-/- mice, cells from 200-day infected mice were able to produce specific IgG2a antibodies, in a T CD4+ cell dependent way. In addition, we verified that CD45R+ cells of subpatent mice, when transferred to CD28-/- mice, secreted higher amounts of specific IgG2a and IgG1 antibodies, comparing to cells of patent mice. So, from this work, we can conclude that the parasite load has a great influence in the early immune response to P. chabaudi malaria and it also affects the generation and/or maintenance of memory B cells. Furthermore, according to our data, at least during the analyzed period, the loss of protective immunity against this parasite does not seem to be influenced by the acute-phase parasite load, but it can be a consequence of the progressive decline of T-cell memory response that occurs in patent and subpatent groups with time of infection.

A exposição limitada ao Plasmodium chabaudi induz proeminente imunidade celular, associada à proteção de células T da apoptose. Este estudo tem como objetivo verificar a influência da carga parasitária na geração e manutenção dos linfócitos T e B de memória ao P. chabaudi. Assim, camundongos C57BL/6 foram submetidos à infecção tratada (subpatente) ou não (patente) com cloroquina após a inoculação de 106 eritrócitos parasitados (EP) e analisados nos dias 0, 20, 60, 120 e 200. Com relação à memória de linfócitos T, no dia 20, as freqüências de células CD4+ memória/ativadas e respondedoras aos EP foram significativamente maiores nos animais do grupo subpatente. Os níveis máximos de IgG2a específica foram encontrados no dia 120 em ambos os grupos. O desafio dos animais com 108 EP mostrou que a imunidade protetora declina progressivamente, mas os grupos ainda são capazes de estabelecer resposta secundária eficiente que elimine o parasita. Assim, podemos concluir que a carga parasitária influencia a fase aguda, mas não impede a geração e manutenção das células T e B de memória. / One of the main characteristics of malaria is the intense policlonal activation of splenic T and B lymphocytes induced by the parasite and the consequent elimination, through apoptosis, of part of these cells. However, the limited exposure to the bloodstage malaria seems to induce a prominent cellular immunity, associated with the protection of T lymphocytes from apoptosis. With this in mind, this study aimed to verify the influence of the parasite load in the generation and maintenance of memory T and B cells specific for Plasmodium chabaudi chabaudi AS. In order to evaluate this idea, C57BL/6 mice were infected with 106 parasitized red blood cells (pRBC) and submitted to a patent (untreated) or subpatent infection (controlled with sub-curative doses of chloroquine every time parasitemia reached 1%). Splenocytes from these mice were analyzed at 20, 60, 120 and 200 days after infection, regarding the pRBC-specific T cell proliferation and the expression of surface molecules, as CD4, CD8, CD62L, CD45RB, CD44, CD45R-B220 and IgG. The parasitemia and the splenocyte phenotype were also monitored after the challenge with 108 pRBC. Regarding T cell memory, at day 20 of infection, the frequencies of effector/activated CD4+ T cells (CD62LLOW CD45RBLOW/HIGH) were significantly increased in animals from the patent group, which was strict linked with the highest cellular activation observed in these animals. On the other hand, the total numbers of pRBCproliferating T (CD4+ and CD8+) cells per spleen were approximately 3-fold increased in subpatent animals, indicating that these cells were protected from apoptosis as a result of the limited exposure to the parasite. However, in both groups, these parameters decreased to values similar to those in controls at day 200. The splenocytes from both groups produced Th1 cytokines in response to pRBC in all times of analysis, but at the early phase of infection, Th2 cytokines were also observed, but without differences between the infected groups. Regarding memory B cells, the frequency of sIgG+ cells was increased at day 20 of infection, when 11% and 9% of CD45R+ cells from patent and subpatent animals were positive, respectively. For both groups, specific IgG2a antibodies attained maximum serum levels at day 120, but at day 200, it is possible to observe a significant decrease of these levels only in the serum of patent mice. Moreover, at day 200 of infection, mice of subpatent group showed significantly higher amounts of IgG2a that recognized the intra-erythrocytic forms of the parasite and the surface of infected erythrocytes. Challenge of mice with 108 pRBC showed that protective immunity progressively decline with time and despite the higher levels of specific antibody in subpatent mice, both groups showed similar protection. In experiments of adoptive transference to CD28-/- mice, cells from 200-day infected mice were able to produce specific IgG2a antibodies, in a T CD4+ cell dependent way. In addition, we verified that CD45R+ cells of subpatent mice, when transferred to CD28-/- mice, secreted higher amounts of specific IgG2a and IgG1 antibodies, comparing to cells of patent mice. So, from this work, we can conclude that the parasite load has a great influence in the early immune response to P. chabaudi malaria and it also affects the generation and/or maintenance of memory B cells. Furthermore, according to our data, at least during the analyzed period, the loss of protective immunity against this parasite does not seem to be influenced by the acute-phase parasite load, but it can be a consequence of the progressive decline of T-cell memory response that occurs in patent and subpatent groups with time of infection.