Comprehensive Immune Profiling Reveals CD56+ Monocytes and CD31+ Endothelial Cells Are Increased in Severe COVID-19 Disease.

Immune response dysregulation plays a key role in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pathogenesis. In this study, we evaluated immune and endothelial blood cell profiles of patients with coronavirus disease 2019 (COVID-19) to determine critical differences between those with mild, moderate, or severe COVID-19 using spectral flow cytometry. We examined a suite of immune phenotypes, including monocytes, T cells, NK cells, B cells, endothelial cells, and neutrophils, alongside surface and intracellular markers of activation. Our results showed progressive lymphopenia and depletion of T cell subsets (CD3+, CD4+, and CD8+) in patients with severe disease and a significant increase in the CD56+CD14+Ki67+IFN-γ+ monocyte population in patients with moderate and severe COVID-19 that has not been previously described. Enhanced circulating endothelial cells (CD45-CD31+CD34+CD146+), circulating endothelial progenitors (CD45-CD31+CD34+/-CD146-), and neutrophils (CD11b+CD66b+) were coevaluated for COVID-19 severity. Spearman correlation analysis demonstrated the synergism among age, obesity, and hypertension with upregulated CD56+ monocytes, endothelial cells, and decreased T cells that lead to severe outcomes of SARS-CoV-2 infection. Circulating monocytes and endothelial cells may represent important cellular markers for monitoring postacute sequelae and impacts of SARS-CoV-2 infection during convalescence and for their role in immune host defense in high-risk adults after vaccination.

Dynamics of T-Lymphocyte Activation Related to Paradoxical Tuberculosis-Associated Immune Reconstitution Inflammatory Syndrome in Persons With Advanced HIV.

Most persons living with HIV (PLWH) experience a significant restoration of their immunity associated with successful inhibition of viral replication after antiretroviral therapy (ART) initiation. Nevertheless, with the robust quantitative and qualitative restoration of CD4+ T-lymphocytes, a fraction of patients co-infected with tuberculosis develop immune reconstitution inflammatory syndrome (TB-IRIS), a dysregulated inflammatory response that can be associated with significant tissue damage. Several studies underscored the role of adaptive immune cells in IRIS pathogenesis, but to what degree T lymphocyte activation contributes to TB-IRIS development remains largely elusive. Here, we sought to dissect the phenotypic landscape of T lymphocyte activation in PLWH coinfected with TB inititating ART, focusing on characterization of the profiles linked to development of TB-IRIS. We confirmed previous observations demonstrating that TB-IRIS individuals display pronounced CD4+ lymphopenia prior to ART initiation. Additionally, we found an ART-induced increase in T lymphocyte activation, proliferation and cytotoxicity among TB-IRIS patients. Importantly, we demonstrate that TB-IRIS subjects display higher frequencies of cytotoxic CD8+ T lymphocytes which is not affected by ART. Moreover, These patients exhibit higher levels of activated (HLA-DR+) and profilerative (Ki-67+) CD4+ T cells after ART commencenment than their Non-IRIS counterparts. Our network analysis reveal significant negative correlations between Total CD4+ T cells counts and the frequencies of Cytotoxic CD8+ T cells in our study population which could suggest the existance of compensatory mechanisms for Mtb-infected cells elimination in the face of severe CD4+ T cell lymphopenia. We also investigated the correlation between T lymphocyte activation profiles and the abundance of several inflammatory molecules in plasma. We applied unsupervised machine learning techniques to predict and diagnose TB-IRIS before and during ART. Our analyses suggest that CD4+ T cell activation markers are good TB-IRIS predictors, whereas the combination of CD4+ and CD8+ T cells markers are better at diagnosing TB-IRIS patients during IRIS events Overall, our findings contribute to a more refined understanding of immunological mechanisms in TB-IRIS pathogenesis that may assist in new diagnostic tools and more targeted patient management.

Potential impact of SARS-CoV-2 infection on the thymus.

Understanding the pathogenesis of certain viral agents is essential for developing new treatments and obtaining a clinical cure. With the onset of the new coronavirus (SARS-CoV-2) pandemic in the beginning of 2020, a rush to conduct studies and develop drugs has led to the publication of articles that seek to address knowledge gaps and contribute to the global scientific research community. There are still no reports on the infectivity or repercussions of SARS-CoV-2 infection on the central lymphoid organ, the thymus, nor on thymocytes or thymic epithelial cells. In this brief review, we present a hypothesis about lymphopenia observed in SARS patients and the probable pathological changes that the thymus may undergo due to this new virus.

Severe COVID-19: what have we learned with the immunopathogenesis?

The COVID-19 outbreak caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a global major concern. In this review, we addressed a theoretical model on immunopathogenesis associated with severe COVID-19, based on the current literature of SARS-CoV-2 and other epidemic pathogenic coronaviruses, such as SARS and MERS. Several studies have suggested that immune dysregulation and hyperinflammatory response induced by SARS-CoV-2 are more involved in disease severity than the virus itself.Immune dysregulation due to COVID-19 is characterized by delayed and impaired interferon response, lymphocyte exhaustion and cytokine storm that ultimately lead to diffuse lung tissue damage and posterior thrombotic phenomena.Considering there is a lack of clinical evidence provided by randomized clinical trials, the knowledge about SARS-CoV-2 disease pathogenesis and immune response is a cornerstone to develop rationale-based clinical therapeutic strategies. In this narrative review, the authors aimed to describe the immunopathogenesis of severe forms of COVID-19.

Lymphopenia and autoimmunity: A double-edged sword.

Lymphopenia is strongly associated with autoimmune diseases. The molecular mechanisms that link both phenomena are still unclear, but certain key pathways have been described. Central tolerance is as important as peripheral. In the earlier, epithelial and dendritic cells play a crucial role in the selection of clones. In the latter, regulatory T cells (Tregs) rise as inductors of anergy in order to prevent the development of autoimmune pathology. In lymphopenic conditions, T cells develop the process of lymphopenia-induced proliferation (LIP). A complex interaction between the major histocompatibility complex (MHC) and the T cell receptor (TCR) makes this process possible. Furthermore, IL-7 can act synergistically or in an independent manner to promote LIP. A lack of Transforming Growth Factor-ß (TGF-ß) was recently described as the second hit needed to develop autoimmunity in a lymphopenic microenvironment, given its actions in Tregs and its interaction with CTLA-4. Regarding autoimmune clinical scenarios, lymphopenia is related to both, systemic and organ-specific diseases. Thus, the molecular study of such patients has been limited and needs to be widened to the pathways shown here to be involved in the development of lymphopenia and autoimmunity.

[End stage renal disease lymphopenia; characterization and clinical correlation]. / Caracterización y correlación clínica de la linfopenia en la enfermedad renal en estadio terminal.

BACKGROUND: Patients with End Stage Renal Disease (ESRD), defined as those in Stage 5 of the Kidney Disease Outcome Quality Initiative (KDOQI) classification, have a number of acquired immune deficiencies secondary to the uremic stage, among them lymphopenia. In the present report, we retrospectively characterized the peripheral blood lymphocyte counts in a group of patients with ESRD and we related lymphopenia to their biochemical parameters and to the presence or absence of infections. METHODS: Medical records from 190 patients in ESRD were selected from 282 medical records of patients being treated between February 2008 and November 2012 for kidney failure at different stages. A number of variables, including lymphocyte counts, biochemical parameters and infections, were analyzed at two different time points: Before and during dialysis. RESULTS: ESRD patients analyzed had a well defined peripheral blood hematological pattern, characterized by severe chronic anemia, normal or elevated leukocyte count and normal or below normal lymphocyte count. The degree of hematological changes correlated with the depth of renal dysfunction and improved with dialysis along with the improvement of urea and creatinine values. CONCLUSIONS: Lymphopenia was present in around half ESRD patients and was associated with increased infections, but they were of the same type as those present in ESRD patients without lymphopenia. Infections were different as those commonly associated with other immune deficiency lymphopenias. The implications of these findings are discussed.

Introducción: los pacientes con insuficiencia renal crónica en etapa terminal (ERET), presentan alteraciones inmunológicas diversas que los hacen más susceptibles a infecciones. Entre las alteraciones reportadas se encuentra la linfopenia. Se han realizado pocos estudios en nuestro medio que muestren la frecuencia y características de esta alteración así como su trascendencia clínica, relacionada con las infecciones que afectan a estos pacientes. Métodos: se analizó una serie de variables, incluyendo los valores de linfocitos y la presencia de infecciones, en un grupo de 190 pacientes con ERET de febrero 2008 a noviembre 2012. Se correlacionan y comparan los valores obtenidos entre ellos en dos momentos de su evolución: antes y durante su tratamiento dialítico. Resultados: en los pacientes con ERET, se obtuvo un perfil hematológico característico, caracterizado por anemia crónica severa, leucocitos totales normales o por arriba de lo normal y linfocitos normales o por debajo de lo normal (linfopenia). El grado de alteración hematológica correlacionó con el grado de afección renal y se corrigió en la medida que se corrigieron las alteraciones bioquímicas relacionadas con la ERET mediante diálisis peritoneal. Conclusiones: la linfopenia se encontró en cerca de la mitad de los pacientes con ERET y se asoció con el incremento de infecciones; el tipo de infecciones fue similar a lo observado en pacientes sin linfopenia y diferente al observado en pacientes con inmunodeficiencias primarias o adquiridas que afectan a los linfocitos.

Applied Protein and Molecular Techniques for Characterization of B Cell Neoplasms in Horses.

Mature B cell neoplasms cover a spectrum of diseases involving lymphoid tissues (lymphoma) or blood (leukemia), with an overlap between these two presentations. Previous studies describing equine lymphoid neoplasias have not included analyses of clonality using molecular techniques. The objective of this study was to use molecular techniques to advance the classification of B cell lymphoproliferative diseases in five adult equine patients with a rare condition of monoclonal gammopathy, B cell leukemia, and concurrent lymphadenopathy (lymphoma/leukemia). The B cell neoplasms were phenotypically characterized by gene and cell surface molecule expression, secreted immunoglobulin (Ig) isotype concentrations, Ig heavy-chain variable (IGHV) region domain sequencing, and spectratyping. All five patients had hyperglobulinemia due to IgG1 or IgG4/7 monoclonal gammopathy. Peripheral blood leukocyte immunophenotyping revealed high proportions of IgG1- or IgG4/7-positive cells and relative T cell lymphopenia. Most leukemic cells lacked the surface B cell markers CD19 and CD21. IGHG1 or IGHG4/7 gene expression was consistent with surface protein expression, and secreted isotype and Ig spectratyping revealed one dominant monoclonal peak. The mRNA expression of the B cell-associated developmental genes EBF1, PAX5, and CD19 was high compared to that of the plasma cell-associated marker CD38. Sequence analysis of the IGHV domain of leukemic cells revealed mutated Igs. In conclusion, the protein and molecular techniques used in this study identified neoplastic cells compatible with a developmental transition between B cell and plasma cell stages, and they can be used for the classification of equine B cell lymphoproliferative disease.

Mycobacterium abscessus pulmonary infection during hepatitis C treatment with telaprevir, peginterferon and ribavirin.

The first generation protease inhibitors has been the mainstay of hepatitis C treatment for the last couple of years, showing marked improvement in sustained virological response, but also increased side effects. Infection has emerged as a common complication of telaprevir and boceprevir in combination with peginterferon and ribavirin, usually caused by common pathogens. We present the case of a 65 years old man who developed a Mycobacterium abscessus pulmonary infection during treatment with telaprevir, peginterferon and ribavirin. The patient was successfully treated with amikacin, imipenem and chlarithromycin. The present case is relevant for increasing awareness for recognition of opportunistic infections and particularly nontuberculous mycobacterial infections in patients receiving triple therapy for chronic hepatitis C, especially in cirrhotic subjects who develop significant lymphopenia.

Lymphopenia as risk factor for development of severe infections in patients with systemic lupus erythematosus: a case-control study.

OBJECTIVES: Hematological abnormalities, particularly lymphopenia, are common in patients with systemic lupus erythematosus (SLE), whether the disease is active or not. The aim of this study is to assess whether lymphopenia (blood counts ≤1000 K/µl) is a risk factor for severe infections in patients with SLE. METHODS: A retrospective case-control study was performed. We reviewed the clinical records of 167 SLE patients throughout a 5-year period. SLE patients with severe infections were compared with those without infection and the presence of lymphopenia was obtained from the blood count previous to the infection date. Also, other clinical and laboratory features as well as immunosuppressive therapy and SLE disease activity index (SLEDAI) were recorded. RESULTS: Univariate analysis shows multiple risk factors for severe infections in SLE, such as lymphopenia, high SLEDAI index, prednisone (PDN) and mycophenolate mofetil treatment and low levels of C3 and C4. Moreover, hydroxychloroquine treatment conferred protection. However, after multivariate analysis, only lymphopenia [odds ratio (OR) 5.2, 95% confidence interval (CI) 2.39-11.3], PDN treatment (OR 4.8, 95% CI 2.1-11.9) and low levels of C3 (OR 2.97, 95% CI 1.1-7.9) remained as independent risk factors. CONCLUSIONS: Our data suggest that lymphopenia, PDN treatment and low levels of C3 are independent risk factors for the development of severe infections in SLE patients, including diverse microorganisms, not only opportunistic infections.

Nasally administered Lactobacillus rhamnosus accelerate the recovery of humoral immunity in B lymphocyte-deficient malnourished mice.

The ability of nasally administered Lactobacillus rhamnosus CRL1505 to accelerate the recovery of respiratory B cell-mediated immunity against pneumococcal infection in replete malnourished mice was evaluated. Weaned mice were malnourished after consumption of a protein-free diet for 21 d. Malnourished mice were fed a balanced conventional diet (BCD) for 7 d (BCD group) or a BCD for 7 d with supplemental L. rhamnosus CRL1505 by the nasal route during the last 2 d (BCD+Lr group). Nonreplete malnourished and normal mice were used as the malnourished (MNC) and the well-nourished (WNC) control groups, respectively. Mice were challenged with Streptococcus pneumoniae at the end of each dietary treatment. The immune response was studied before the challenge and at different times postinfection. The MNC mice had less resistance to pneumococcal infection, fewer mature and immature B cells in lung and spleen, and a reduced production of specific antibodies compared with WNC mice. The BCD treatment did not induce a complete normalization of the number B cell populations and antibody amounts. However, the BCD+Lr group had normal numbers of spleen and lung B cells. Moreover, the BCD+Lr mice had a significantly lower susceptibility to S. pneumoniae infection and higher amounts of anti-pneumococcal antibodies. Although further studies are necessary to clarify the effect of malnutrition and nasally administered lactobacilli in other immune cell populations involved in the protection against respiratory pathogens, this work gives evidence of the importance of using nasal priming with probiotics to accelerate the recovery of respiratory immunity in immunocompromised malnourished hosts.

Low CD40L levels and relative lymphopenia in narcoleptic patients.

Narcolepsy has been studied as a possible autoimmune disease for many years, and recent findings lend more credence to this belief. Although recent and important advances have been done, no study has analyzed the role of the CD40L in patients with narcolepsy. The purpose of this study was to assess CD40L levels, CD3, TCD4, TCD8, CD19, and CD56 lymphocytes, as well as levels of tumor necrosis factor-α and interleukin-6 in narcoleptic patients. We quantified the levels of CD40L, different types of lymphocytes, and levels of tumor necrosis factor-α and interleukin-6 in narcoleptic patients and control subjects. Narcoleptic patients had lower levels of CD40L. Total lymphocytes; CD3, and TCD4 were lower than in the control group. Our findings highlight the important role of CD40L in narcolepsy.

Quantitative and functional profiles of CD4+ lymphocyte subsets in systemic lupus erythematosus patients with lymphopenia.

Lymphopenia is a common clinical manifestation in patients with systemic lupus erythematosus (SLE). However, its physiopathogenic role and the contribution of different T cell subsets in this setting have not been addressed fully. The aim of this study was to characterize T cell subsets quantitatively and functionally and their association with lymphopenia and azathioprine treatment in SLE. We included 84 SLE patients and 84 healthy controls and selected 20 patients for a 6-month longitudinal analysis. Peripheral blood mononuclear cells were isolated, and T cell subsets were analysed by flow cytometry. Functional analyses included autologous and allogeneic co-cultures of T cells. Our data show persistently lower absolute numbers of CD4(+) CD25(high) T cells [regulatory T cells (T(regs) )] (1·9 versus 5·2, P < 0·01) and CD4(+) CD69(+) T cells (3·2 versus 9·3, P = 0·02) and higher activity scores (4·1 versus 1·5, P = 0·01) in SLE patients with lymphopenia compared with those without lymphopenia. Lymphopenia increased the risk for decreased numbers of CD4(+) CD25(high) cells (relative risk 1·80, 95% confidence interval 1·10-2·93; P = 0·003). In addition, azathioprine-associated lymphopenia was characterized by decreased absolute numbers of CD4(+) CD69(+) and CD4(+) interleukin (IL)-17(+) cells compared to disease activity-associated lymphopenia. Functional assays revealed that SLE effector T cells were highly proliferative and resistant to suppression by autologous T(regs) . In summary, lymphopenia was associated with deficient numbers of CD4(+) CD25(high) and CD4(+) CD69(+) cells and resistance of effector T cells to suppression by T(regs) , which could contribute to the altered immune responses characteristic of SLE. Furthermore, azathioprine treatment was associated with decreased numbers of CD4(+) CD69(+) and CD4(+) IL-17(+) cells and diminished T(reg) suppressive activity.

Autoantibodies against galectin-8: their specificity, association with lymphopenia in systemic lupus erythematosus and detection in rheumatoid arthritis and acute inflammation.

The role of autoantibodies in the pathogenesis of systemic lupus erythematosus (SLE) has not been completely defined. From more than a hundred autoantibodies described in SLE, relatively few have been associated with clinical manifestations. The glycan-binding proteins of the galectin family can modulate the immune system. Anti-galectin autoantibodies thus could have functional and/or pathogenic implications in inflammatory processes and autoimmunity. We previously reported function-blocking autoantibodies against galectin-8 (Gal-8) in SLE. Here we tested these autoantibodies against a series of other human galectins and demonstrated their specificity for Gal-8, being detectable in 23% of 78 SLE patients. Remarkably, they associated with lymphopenia (50% of 18 anti-Gal-8-positive versus 18% of 60 anti-Gal-8-negative cases, Fisher's Exact test two-tailed: P < 0.012). Lymphopenia is a common clinical manifestation in SLE, yet of unknown mechanism. In addition, six of eight patients with both lymphopenia and malar rash had anti-Gal-8 in their sera. Occurrence of these autoantibodies was not confined to SLE as we also found them in sera of patients with rheumatoid arthritis (16%) and septicemia (20%). This study thus establishes occurrence of specific anti-Gal-8 autoantibodies in autoimmune rheumatic diseases and in acute inflammation, with an apparent association to a clinical subset in SLE.

Pathogenic effector T cell enrichment overcomes regulatory T cell control and generates autoimmune gastritis.

Regulatory T cells (Treg) deficiency leads to a severe, systemic, and lethal disease, as showed in immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome patients, and scurfy mouse. Postneonatal thymectomy autoimmune gastritis has also been attributed to the absence of Tregs. In this case however, disease is mild, organ-specific, and, more important, it is not an obligatory outcome. We addressed this paradox comparing T cell compartments in gastritis-susceptible and resistant animals. We found that neonatal thymectomy-induced gastritis is not caused by the absence of Tregs. Instead of this, it is the presence of gastritogenic T cell clones that determines susceptibility to disease. The expansion of such clones under lymphopenic conditions results in a reduced Treg:effector T cell ratio that is not enough to control gastritis development. Finally, the presence of gastritogenic clones is determined by the amount of gastric Ag expressed in the neonatal thymus, emphasizing the importance of effector repertoire variability, present even in genetically identical subjects, to organ-specific autoimmune disease susceptibility.

Susceptibility of neonatal T cells and adult thymocytes to peripheral tolerance to allogeneic stimuli.

We studied the tolerization of neonatal thymocytes (NT), neonatal splenocytes (NS) and adult thymocytes (AT), transferred to syngeneic nude (nu/nu) hosts previously injected with semi-allogeneic splenocytes, without any supportive immunosuppressive treatment. This protocol allows the study of peripheral tolerance in the absence of the thymus. BALB/c neonatal T cells and ATs were able to expand in syngeneic BALB/c nu/nu mice and functionally reconstituted an allogeneic response, rejecting (BALB/c x B6.Ba) F1 splenocytes transferred 3-4 weeks after injection of BALB/c cells. However, if (BALB/c x B6.Ba) F1 cells were injected into BALB/c nude hosts 30 days before transfer of NT, NS or AT cells, the F1 population was preserved and specific tolerance to B6 allografts was established. Furthermore, transfer to lymphopenic F1 nu/nu showed that tolerance could be established only for neonatal populations, showing that unique properties of neonatal T cells allow their tolerization in both lymphopenic and non-lymphopenic conditions, in the absence of suppressive immunotherapy. These results bring empirical support to the possibility of T-cell engraftment in immunodeficient patients showing partial identity with donor major histocompatibility complex (MHC) genes; the manipulation of immunological maturity of donor T cells may be the key for successful reconstitution of immunocompetence without induction of graft-versus-host disease.

Normal hematopoiesis is maintained by activated bone marrow CD4+ T cells.

CD4(+) T cells produce hematopoietic-related cytokines and are essential for hematopoiesis stimulation during infection and hematologic recovery after bone marrow transplantation. However, it remains unclear if T cells are necessary to maintain normal hematopoiesis. We report here that, in T-cell-deficient mice, terminal differentiation of myeloid progenitors is defective, resulting in very low levels of granulocytes in the periphery. Hematopoiesis is restored after thymus graft or reconstitution with CD4(+) T cells but not CD8(+) T cells. Bone marrow CD4(+) T cells have an activated phenotype and produce cytokines, apparently, in the absence of exogenous stimulation. Transgenic mice carrying T-cell receptor specific for an ovalbumin peptide presented in the context of a specific class II molecule (I-A(d)) (DO11.10 RAG(-/-)) show the same hematopoietic deficiency as athymic mice. Their bone marrow CD4(+) T cells are not activated, suggesting that hematopoiesis maintenance requires the presence of cognate antigen in order to activate bone marrow T-helper cells. In fact, priming of transgenic mice with ovalbumin restores normal hematopoiesis. The data show that the current concept of "normal hematopoiesis" does not reflect a basal bone marrow activity, but it is an antigen-induced state maintained by constant activation of bone marrow CD4(+) T cells.

Immunodeficiency and infections in ataxia-telangiectasia.

OBJECTIVE: To characterize the immunodeficiency in ataxia-telangiectasia (A-T) and to determine whether the immunodeficiency is progressive and associated with increased susceptibility to infections. STUDY DESIGN: Records of 100 consecutive patients with A-T from the Johns Hopkins Ataxia-Telangiectasia Clinical Center (ATCC) were reviewed. RESULTS: Immunoglobulin (Ig) deficiencies are common, affecting IgG4 in 65% of patients, IgA in 63%, IgG2 in 48%, IgE in 23%, and IgG in 18%. Lymphopenia affected 71% of patients, with reduced B-lymphocyte number in 75%, CD4 T lymphocytes in 69%, and CD8 T lymphocytes in 51%. There was no trend for increased frequency or severity of immune abnormalities with age. Recurrent upper and lower respiratory tract infections were frequent: otitis media in 46% of patients, sinusitis in 27%, bronchitis in 19%, and pneumonia in 15%. Sepsis occurred in 5 patients, in 2 patients concurrent with cancer chemotherapy. Warts affected 17% of patients, herpes simplex 8%, molluscum contagiosum 5%, candidal esophagitis 3%, and herpes zoster 2%. Uncomplicated varicella infection occurred in 44% of patients; 2 patients had more than one clinical episode. No patient had Pneumocystis jerovici pneumonia or a complication of live viral vaccine. CONCLUSIONS: In spite of the high prevalence of laboratory immunologic abnormalities, systemic bacterial, severe viral, and opportunistic infections are uncommon in A-T. Cross-sectional analysis suggests that the immune defect is rarely progressive.

Acute chylothorax in children: selective retention of memory T cells and natural killer cells.

OBJECTIVE: To assess for immunodeficiency in patients with hypogammaglobulinemia in the setting of draining acute chylothorax. STUDY DESIGN: Humoral and cellular immunity was evaluated in 8 patients with chylothorax. Chylous fluid was also analyzed to document cellular losses. Data regarding clinical course and immunologic characteristics were reviewed retrospectively. RESULTS: All patients had hypogammaglobulinemia (IgG=179+/-35 mg/dL) as well as lymphopenia (985+/-636 cells/mm(3)). T cells were decreased and natural killer cells increased in peripheral blood. The converse was found in chylous fluid. The ratio of CD3+/CD45RA+ naive: CD3+/CD45RO+ memory T cells was greater in chyle than in peripheral blood. In vitro proliferative responses to antigens and mitogens were similar to control subjects, and previously immunized patients maintained evidence of protective vaccine-specific humoral immunity. To treat hypogammaglobulinemia, patients received intravenous immunoglobulin (IVIG) to maintain IgG within normal range; 6 of 8 patients had serious infections before receiving IVIG compared with 4 of 8 patients during the period of IVIG administration. CONCLUSION: Draining chylothorax resulted in IgG and lymphocyte depletion with preferential retention of memory T cells and natural killer cells in the circulation. Overall, protective-specific antibody levels and T cell function were maintained. IVIG administration did not lead to discernible protection from infectious complications in this small group of patients.