Contribution of T cell subsets to the pathophysiology ofPneumocystis-related immunorestitution disease

Abstract

.-Immune-mediated lung injury is an important component of Pneumocystis pneumonia (PcP)-related immunorestitution disease (IRD). However, the individual contribution of CD4 ϩ and CD8 ϩ T cells to the pathophysiology of IRD remains undetermined. Therefore, IRD was modeled in severe combined immunodeficient mice, and specific T cell depletion was used to determine how T cell subsets interact to affect the nature and severity of disease. CD4 ϩ cells were more abundant than CD8 ϩ cells during the acute stage of IRD that coincided with impaired pulmonary physiology and organism clearance. Conversely, CD8 ϩ cells were more abundant during the resolution phase following P. carinii clearance. Depletion of CD4 ϩ T cells protected mice from the acute pathophysiology of IRD. However, these mice could not clear the infection and developed severe PcP at later time points when a pathological CD8 ϩ T cell response was observed. In contrast, mice depleted of CD8 ϩ T cells efficiently cleared the infection but developed more severe disease, an increased frequency of IFN-␥-producing CD4 ϩ cells, and a prolonged CD4 ϩ T cell response than mice with both CD4 ϩ and CD8 ϩ cells. These data suggest that CD4 ϩ T cells mediate the acute respiratory disease associated with IRD. In contrast, CD8 ϩ T cells contributed to neither lung injury nor organism clearance when CD4 ϩ cells were present, but instead served to modulate CD4 function. In the absence of CD4 ϩ cells, CD8 ϩ T cells produced a nonprotective, pathological immune response. These data suggest that the interplay of CD4 ϩ and CD8 ϩ T cells affects the ultimate outcome of PcP-related IRD.inflammation; pulmonary physiology; acquired immune deficiency syndrome PNEUMOCYSTIS carinii IS an opportunistic fungus that causes pneumonia in immune-compromised patients (37), including patients with acquired immune deficiency syndrome (AIDS) (29), patients undergoing chemotherapy, and patients receiving treatment with immunosuppressive drugs during organ transplantation (34). Although exposure to P. carinii is nearly universal, as demonstrated by the appearance of anti-P. carinii antibody in 85% of children by the age of 20 mo (35), a period of immunosuppression is essential for the development of clinical disease (15,34). Several studies have demonstrated a positive correlation between the degree of inflammation and the severity of disease (4,23,36), suggesting that the pathogenesis of Pneumocystis pneumonia (PcP) is primarily inflammatory in nature, in that infection with P. carinii is necessary to cause pneumonia, but certain aspects of the immune response against P. carinii are responsible for the associated pathophysiology (30, 39). For example, AIDS patients who demonstrate a rapid recovery of CD4 ϩ T lymphocytes after institution of combined antiretroviral therapy may develop pulmonary decompensation in response to preexisting pulmonary infections, including P. carinii (26). This clinical syndrome has been termed "immunorestitution disease" (IRD) (9). At least one study that examined t...

Neither Classical nor Alternative Macrophage Activation Is Required for Pneumocystis Clearance during Immune Reconstitution Inflammatory Syndrome

“…5). Data from previous reports by Swain et al and Bhagwat et al are consistent with our observation of exacerbated CD4 ϩ T cell-mediated IRIS when CD8 ϩ T cells are absent during recovery of host immune function (16,27). Although CD8 ϩ T cells have long been regarded as cytotoxic cells, the CD8 ϩ T cells recruited to the lung during IRIS appear to play a more regulatory role by limiting the CD4 ϩ T cell response to Pneumocystis infection (34,35).…”

“…The mouse model of PcP-related IRIS was used, as described previously (18,27). RAG2 Ϫ/Ϫ , RAG2/IL-4R␣ Ϫ/Ϫ , and RAG2/IFN-␥R Ϫ/Ϫ mice were intratracheally inoculated with 5 ϫ 10 5 purified Pneumocystis organisms based on cyst counts.…”

“…Dynamic lung compliance and lung resistance were measured in live, ventilated mice by using a whole-body plethysmograph (Buxco Electronics Inc., Wilmington, NC) connected to a Harvard rodent ventilator (Harvard Apparatus, Southnatic, MA), as described previously (18,27). Respiratory rates were measured by using whole-body unrestrained chambers, and data were collected and analyzed by using the Biosystems XA software package (Buxco Electronics Inc.).…”

“…Unstimulated BAL fluid cells were incubated with Fc block (BD Biosciences, San Diego, CA) and then with fluorescently labeled antibodies against the surface markers CD4 (RM4-5), CD8 (53-6.7), CD11c (HL3), GR-1 (RB6-8C5), and CD3 (500A2). Some BAL fluid cells were stimulated with 50 to 100 ng/ml phorbol myristate acetate (PMA) and 1 mM ionomycin for 4 h in the presence of GolgiPlug (BD Biosciences), as described previously (27). Stimulated cells were incubated with Live/Dead Fixable Aqua stain (Molecular Probes, Eugene, OR) for 30 min, followed by surface staining.…”

Pneumocystis

“…The immune reconstituted SCID mouse model of PCP is similar to the IRIS presentation of PCP in human patients, and provides a model for elucidating mechanisms of PCP-related IRIS. Recent discoveries using this model have determined that CD4 þ T cells are critical for mediating immunopathogenesis, whereas CD8 þ T cells serve a regulatory function by limiting the CD4 þ T-cell response (Bhagwat et al 2006;Swain et al 2006). Pharmacological manipulation of the organism in vivo found that the cyst form of Pneumocystis, which contains proinflammatory cell wall components, drives immunopathogenesis during IRIS (Linke et al 2013).…”