Pneumocystis carinii pneumonitis in patients with hypogammaglobulinemia and intact T cell immunity

Genetic analysis of patients with defects in early B-cell development

Approximately 85% of patients with defects in early B-cell development have X-linked agammaglobulinemia (XLA), a disorder caused by mutations in the cytoplasmic Bruton's tyrosine kinase (Btk). Although Btk is activated by cross-linking of a variety of cell-surface receptors, the most critical signal transduction pathway is the one initiated by the pre-B cell and B-cell antigen receptor complex. Mutations in Btk are highly diverse, and no single mutation accounts for more than 3% of patients. Although there is no strong genotype/phenotype correlation in XLA, the specific mutation in Btk is one of the factors that influences the severity of disease. Mutations in the components of the pre-B cell and B-cell antigen receptor complex account for an additional 5-7% of patients with defects in early B-cell development. Patients with defects in these proteins are clinically indistinguishable from those with XLA. However, they tend to be younger at the time of diagnosis, and whereas most patients with XLA have a small number of B cells in the peripheral circulation, these cells are not found in patients with defects in micro heavy chain or Igalpha. Polymorphic variants in the components of the pre-B cell and B-cell receptor complex, particularly micro heavy chain and lambda5, may contribute to the severity of XLA.

Kinase mutant Btk results in atypical X-linked agammaglobulinaemia phenotype

X-linked agammaglobulinaemia (XLA) is a B cell humoral abnormality arising from mutations in the gene encoding Bruton's tyrosine kinase (Btk). The phenotype of XLA can be variable, with some individuals having a less severe immunophenotype, although in most cases this cannot be correlated with the Btk mutation or expression of Btk protein. In this study we describe clinical and immunological heterogeneity within the same pedigree. Analysis of the genetic defect identified a missense mutation in the kinase domain of Btk which, unusually, preserved Btk protein expression but at reduced levels, and also considerably diminished autophosphorylation activity. Structural analysis of the effect of this mutation on the kinase domain suggests that this mutation is not an integral part of the ATP or substrate binding domains but may affect the interaction of the kinase domain with its own kinase domain and other substrates. Together, these data may provide an explanation for the variable XLA phenotype.

CD4+ and CD8+ T-lymphocytopenia in a filly with Pneumocystis carinii pneumonia

Decreased proportion of CD4+ and CD8+ T lymphocytes in peripheral blood likely contributed to susceptibility to Pneumocystis carinii in a foal. Cytological evaluation of bronchoalveolar lavage was required for identification of the pathogen and serial flow-cytometric analysis of peripheral blood lymphocytes documented transient low expression of CD4+ and CD8+ T lymphocytes. Although immunodeficiency is uncommon, it must be included in the differential diagnosis for patients suffering from chronic or opportunistic infections and may provide an indication for immunostimulant therapy.

Antibody to Pneumocystis carinii protects rats and mice from developing pneumonia

Well-proven mouse and rat models were used to show that polyclonal antisera to Pneumocystis carinii protect against P. carinii pneumonia. Antibodies were obtained from animals that were allowed to recover from severe P. carinii pneumonia after immunosuppression had been stopped and which then were given a booster injection of P. carinii from the same animal species. Mice immunosuppressed with corticosteroids or antibodies to L3T4+ lymphocytes (which are comparable to CD4 cells of humans) and transtracheally inoculated with mouse P. carinii did not develop P. carinii pneumonia if they were passively immunized with antiserum, while mice immunosuppressed and inoculated by identical procedures but not given antibodies developed severe infections. Rats immunosuppressed with corticosteroids and inoculated with rat P. carinii had less severe infections if they were given rat anti-P. carinii antisera. The polyclonal antisera developed in mice provided greater protection for the mice than the polyclonal rat antisera did for the rats; however, the potencies and compositions of the antisera were not quantitated and probably differed. Since both rats and mice can be protected from P. carinii infections with polyclonal antisera, it may be possible to develop vaccines that will elicit protective antibodies in humans.

Analysis of cytokine mRNA profiles in the lungs of Pneumocystis carinii-infected mice

Severe combined immunodeficient (scid) mice lack functional CD4+ lymphocytes, and therefore develop life-threatening Pneumocystis carinii infection. However, when scid mice are immunologically reconstituted with spleen cells, including CD4+ cells, a protective inflammatory response is mounted against the organism. To determine whether these lymphocytes induce elevated cytokine mRNA levels in response to P. carinii infection, steady-state levels of cytokine mRNAs were measured in the lungs of both reconstituted and unaltered scid mice. Despite significant numbers of organisms and the presence of functional alveolar macrophages in the lungs of 8- and 10-wk-old scid mice, there was neither evidence of pulmonary inflammation, nor increased proinflammatory cytokine expression. However, when 8-wk-old scid mice were immunologically reconstituted, signs of intense, focal pulmonary inflammation were observed, and levels of interleukin (IL)-1alpha, IL-1beta, IL-3, IL-6, interferon-gamma (IFN-gamma), tumor necrosis factor (TNF)-alpha, and TNF-beta mRNAs were all significantly elevated. Cytokine expression was increased at day 10 post-reconstitution (PR), maximal at day 12 PR, and returned to baseline by day 22 PR. In situ hybridization demonstrated that at day 12 PR, increased IL-1beta and TNF-alpha expression was localized to sites of intense inflammation and focal P. carinii colonization. Many of the cells expressing high levels of IL-1beta and TNF-alpha in these regions were in direct contact with organisms, or contained degraded organisms within their cytoplasm. Thus, even though functional macrophages are present in scid mice, CD4+ T cells are required for proinflammatory cytokine expression, which is associated with the generation of a protective inflammatory response at sites of P. carinii infection.

Pneumocystis carinii

Improved understanding of Pneumocystis carinii, in particular the widespread use of chemoprophylaxis, has resulted in a declining incidence of infection in patients infected with HIV since the late 1980s. Despite these advances, P. carinii pneumonia continues to represent an important cause of pulmonary disease in HIV-seropositive individuals who do not receive chemoprophylaxis or when breakthrough episodes occur. This article reviews the history, biology, clinical manifestations, prognostic markers, therapy, and chemoprophylaxis of P. carinii pneumonia in HIV-seropositive patients.

An outbreak of Pneumocystis carinii pneumonia in children with malignancy

An outbreak of Pneumocystis carinii pneumonia (PCP) in three patients within a 6 week period was reported. Two patients had acute lymphoblastic leukaemia and one had brain-stem glioma. They shared common features of immunosuppression and absence of cotrimoxazole prophylaxis and had been nursed in the same room. The severity of PCP and its response to treatment may be related to the degree of immunosuppression. Because of the morbidity and mortality of PCP, chemoprophylaxis should be given to all at-risk cases. Furthermore, isolation of patients with PCP should be considered in view of increasing evidence of nosocomial transmission.

Both immunity and hyperresponsiveness to Pneumocystis carinii result from transfer of CD4+ but not CD8+ T cells into severe combined immunodeficiency mice

The opportunistic pathogen Pneumocystis carinii (Pc) is considered to be the leading cause of morbidity in patients with AIDS. It is important, therefore, to determine the immunological mechanisms of resistance to Pc. We have taken advantage of the lack of both T and B lymphocytes in severe combined immunodeficiency (scid) mice to determine the critical factors in resistance to spontaneously acquired Pc pneumonia. Using adoptive transfer of unfractionated or fractionated lymphocyte subsets or hyperimmune serum from congenic normal donors, we have demonstrated that effective immunity to Pc results from the action of CD4+ but not CD8+ T cells (in the absence of antibody) or from humoral immunity (in the absence of T cells). However, responses of CD4+ T cells (but not antibody) to already well-established burdens of Pc are often accompanied by a fatal hyperinflammatory reaction. The activity of CD4+ T cells against Pc thus illustrates a broadly applicable principle that T cell immunity represents a critical balance between consequences beneficial and harmful to the host.

Specific T-cell response to a Pneumocystis carinii surface glycoprotein (gp120) after immunization and natural infection

T cells have been shown to be important in recovery from Pneumocystis carinii pneumonitis, although no specific antigen of P. carinii has been defined as containing T-cell epitopes. P. carinii has an abundant mannosylated surface glycoprotein of approximately 120 kDa (gp120) which induces a prominent host antibody response in experimental animals after exposure to P. carinii in the environment or after recovery from P. carinii pneumonitis. P. carinii gp120 was purified from infected lungs by lectin affinity chromatography. Standard in vitro lymphocyte stimulation assays using purified gp120 and control normal lung preparations were performed on isolated T cells obtained from BALB/c mice after immunization with P. carinii-infected crude lung homogenates or lectin-purified gp120. Lymphocytes from reconstituted severe combined immunodeficient mice which had recovered from naturally acquired P. carinii pneumonitis were also tested. A specific T-cell response was elicited by gp120 after immunization with P. carinii gp120 and after recovery from P. carinii pneumonitis. In addition, the mice developed a strong antibody response to gp120 as ascertained by Western blot (immunoblot). These data suggest that gp120 may be important in the recognition of P. carinii by T cells.

Pneumocystis carinii, an opportunist in immunocompromised patients

Pneumocystis carinii has been recognized as a cause of pneumonia in immunocompromised patients for over 40 years. Until the 1980s, Pneumocystis pneumonia (pneumocystosis) was most often seen in patients undergoing chemotherapy for malignancy or transplantation. Infection could be prevented by trimethoprim-sulfamethoxazole prophylaxis; thus, it was an uncommon clinical problem. With the onset of the AIDS epidemic, Pneumocystis pneumonia has become a major problem in the United States because it develops in approximately 80% of patients with AIDS and because almost two-thirds of patients have adverse reactions to anti-Pneumocystis drugs. Thus, physicians and laboratories in any community may be called upon to diagnose and provide care for patients with Pneumocystis pneumonia. The classification of the organism is currently controversial, but it is either a protozoan or a fungus. P. carinii appears to be acquired during childhood by inhalation and does not cause clinical disease in healthy persons but remains latent. If the person becomes immunosuppressed, the latent infection may become activated and lead to clinical disease. Damage of type I pneumocytes by Pneumocystis organisms leads to the foamy alveolar exudate which is characteristic of the disease. Diagnosis is established by morphologic demonstration of Pneumocystis organisms in material from the lungs. Current efforts to find better anti-Pneumocystis drugs should provide more effective therapy and prophylaxis.

Common variable hypogammaglobulinemia, recurrent Pneumocystis carinii pneumonia on intravenous gamma-globulin therapy, and natural killer deficiency

A toddler with common variable hypoimmunoglobulinemia (CVH), inflammatory bowel disease, and recurrent Pneumocystis carinii pneumonia (PCP) on intravenous gammaglobulin (IVIG) replacement was evaluated for a combined cellular immunodeficiency. He had a normal number of circulating T-cells, natural killer (NK) cells, T-cell subset percentages, and his peripheral blood mononuclear (PBM)-derived B-cell number was low. PBM mitogen blastogenesis and mixed lymphocyte reaction (MLR) were normal. MLR activated T-cells expressed class I and II MHC antigens, interleukin 2 (IL-2), and B-cell growth factor (IL-5)-related receptors. The patient's T-cells induced control B-cell maturation with pokeweed mitogen (PWM-PC), and did not suppress PWM-PC production by allogeneic PBM. Bone marrow (BM) CD19+ B-cell number varied between 10 and 44% of all PBM, and the BM B-cell-enriched fraction failed to differentiate to PWM-PC with autologous or allogeneic T-cell help. The NK activity assayed using K562 target cells was deficient, 9.2 x 7.7% (6.9-9.2%) pt, control 35.9 x 35.8% (16.3-67.2% +/- 12.8). In the presence of interferon-alpha, 800 U/ml, the patient's NK activity increased to 17.2 x 14.9% (12.6-17.2%), control 35.9 x 51.0% (36.5-72.3% +/- 12.0). The patient's cell-mediated lympholysis of HLA nonidentical, allogeneic stimulators was normal. Maintaining trough serum IgG levels above 500 mg/dl was required to suppress recurrent PCP. This functional NK deficiency may be relevant to the development of recurrent PCP in IVIG-treated CVH patients.

Infectious complications of the primary immunodeficiencies

The primary manifestation of the immunodeficiencies is undue susceptibility to infection. This means too many, too severe, too prolonged, too complicated and too unusual infections. Infections in immunodeficiency have a characteristic cause depending on the nature of the immune deficiency. Antibody deficiencies are associated with infections with gram-positive infections. Cellular immune deficiencies are associated with mycobacterial, protozoan, fungus, virus, and opportunistic bacterial infection. Phagocytic disorders are associated with staphylococcal, fungal, and gram-negative organisms. Complement disorders are associated by neisserial infections. Infections have also been implicated in the pathogenesis of some immunodeficiencies in some circumstances. These include human T lymphotropic virus type III (HTLV-III), rubella virus, cytomegalovirus, and Epstein-Barr virus. Several infectious syndromes in specific immunodeficiencies have been identified. Examples include enteric cytopathic human orphan (ECHO) virus encephalitis in agammaglobulinemia, and meningococcal meningitis in C6 deficiency. Infections can also be induced by live vaccines given in immunodeficiency (e.g., paralytic polio in agammaglobulinemia.) Unusual infectious syndromes will be illustrated including parainfluenza infection in severe combined and immunodeficiency, Legionella pneumonia in chronic granulomatous disease, and Cryptosporidium infection in hyper-IgM immunodeficiency.