Analysis of murine lymphocyte subpopulations by dual-color flow cytometry: technical considerations and specificities of monoclonal antibodies directed against surface markers

Changes in circulating lymphocyte subpopulations and mitogen-stimulated response in a rat infusion model of intra-abdominal infection

OBJECTIVE

To describe the alterations in circulating concentrations of immune cells as well as in in vitro mitogen-stimulated response in a recently developed rat model of intra-abdominal infection.

DESIGN

Randomized, controlled study.

SETTING

Government research facility.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Infected animals received an intraperitoneal infusion of 6.0 x 10(8) colony forming units of Escherichia coli during 12 hrs, whereas control rats received a sterile inoculum. All experimental animals underwent laparotomy and peritoneal lavage at the end of the infusion period. Blood samples were obtained 12 hrs, 36 hrs, or 7 days after the onset of infusion. Splenocytes were concomitantly harvested and assayed for response to the mitogens phytohemagglutinin (PHA), concanavalin A (Con A), and lipopolysaccharides, as well as for production of interleukin (IL)-2.

MEASUREMENTS AND MAIN RESULTS

Infected rats showed a marked leukopenia (-82% for 36 hrs), with leukocyte counts returning to normal at 7 days. They also developed a marked lymphocytopenia throughout the study; this was achieved through comparable reductions in circulating T and B cells. Con A responses in both groups were similar for 7 days. In contrast, splenocytes from infected animals showed reduced responses to lipopolysaccharides (-64%) and PHA (-30%) for 36 hrs compared with control splenocytes. IL-2 production from mitogen-stimulated splenocytes was suppressed in infected rats to 66% of that of control rats for 7 days. Suppressed PHA responses were not restored to control values in the presence of IL-2. For all of the parameters assessed, control animals showed either no significant changes or relatively fewer changes than infected rats.

CONCLUSIONS

This model of intra-abdominal infection is associated with changes in circulating concentrations of immune cells as well as with temporary functional defects in B and T cells, consistent with those often observed in patients with peritonitis. However, the role of IL-2 in limiting the adverse effects of infection in this experimental model seems to be limited. This model may be a useful tool in furthering our understanding of the pathophysiology of intra-abdominal infections and in assessing the efficacy of new therapeutic modalities.

Increased oxygen tensions influence subset composition of the cellular immune system in aged mice

In acute and chronic experiments, each of eight groups of aged mice were assigned separately to different pressures of oxygen to which it was to be exposed. Lymphocytes from spleen, thymus, and peripheral blood were analyzed following oxygen exposure. Subset populations changed depending on the oxygen tension. Variable changes were observed in total numbers of lymphocytes, lymphocyte subsets, B cells, and macrophages depending on the organ studied and the oxygen pressure to which the mice were exposed. There were differences between acute and chronic exposure suggestive of adaptation to environmental stressors. The suggestion is made that the immune system has a reserve capacity that can be influenced by oxygen and, thereby, theoretically capable of being pharmacologically manipulated to assist patients with altered immune systems to promote defense mechanisms or, under certain circumstances, reduce autoimmunity. It is hypothesized that an underlying hypoxia may be involved in the age-associated decline in the immune system.

Increased oxygen tensions modulate the cellular composition of the adaptive immune system in BALB/c mice

In acute and chronic experiments, each of eight groups of young mice were assigned separately to different pressures of oxygen to which it was to be exposed. Lymphocytes from spleen, thymus, and peripheral blood were analyzed following oxygen exposure. Subset populations changed depending on the oxygen tension. Blood lymphocyte populations reflected lymphocyte changes in thymus or spleen. Thus, a full understanding of the pharmacological effects of hyperbaric oxygen, requires a knowledge of simultaneous effects of increased oxygen pressures on the various compartments comprising the immune system.

Defective T-cell surface antigen expression after mitogen stimulation. An index of lymphocyte dysfunction after controlled murine injury

Murine spleen T-cell activation in lectin-stimulated cultures after 25% body surface area burn injury or hind-limb amputation was studied by measuring the temporal expression of cell surface markers using monoclonal antibodies and two-color flow cytometry. Lymphocyte activation has been shown to be accompanied by the appearance of new surface antigens, including Interleukin-2 (IL-2) deceptor (IL-2R) and Ia, and emergence of cells that coexpress helper (Th) and suppressor (Ts) surface markers. IL-2R has been shown to appear early on stimulated cells, before DNA synthesis, whereas Ia appears later. Surface markers (L3T4, Lyt2, Ia, and IL-2R) were analyzed at time 0 and after 24, 48, and 72 hours of mitogen-stimulated culture. The appearance of IL-2R and Ia on Th (L3T4+) and Ts (Lyt-2+) populations was markedly depressed after burn injury, but minimal changes were seen after musculoskeletal injury. In addition, coexpression of L3T4/Lyt2 antigens was markedly reduced in burn-derived cells. Serum from burn-injured animals caused depression of surface antigen expression by stimulated normal cells. Recombinant IL-2, when added to burn-derived cell cultures, did not increase expression of these surface markers during culture, nor did it improve proliferation.