Association of decreased natural and antibody-dependent cellular cytotoxicity and production of natural killer cytotoxic factor and interferon in neonates

Dysregulated Mucosal Immunity and Associated Pathogeneses in Preterm Neonates

Many functions of the immune system are impaired in neonates, allowing vulnerability to serious bacterial, viral and fungal infections which would otherwise not be pathogenic to mature individuals. This vulnerability is exacerbated in compromised newborns such as premature neonates and those who have undergone surgery or who require care in an intensive care unit. Higher susceptibility of preterm neonates to infections is associated with delayed immune system maturation, with deficiencies present in both the innate and adaptive immune components. Here, we review recent insights into early life immunity, and highlight features associated with compromised newborns, given the challenges of studying neonatal immunity in compromised neonates due to the transient nature of this period of life, and logistical and ethical obstacles posed by undertaking studies newborns and infants. Finally, we highlight how the unique immunological characteristics of the premature host play key roles in the pathogenesis of diseases that are unique to this population, including necrotizing enterocolitis and the associated sequalae of lung and brain injury.

Natural killer cell responses to infections in early life

Natural killer (NK) cells are an important component of innate immune responses to infectious diseases. They mediate protection by being able to rapidly lyse infected cells and produce cytokines (primarily interferon-γ) that shape innate and adaptive immune responses. This review summarizes current knowledge on the phenotype and functional abilities of NK cells from healthy newborns/infants and on NK cell responses against viral, bacterial and protozoan infections in early life. Interestingly, NK cell blood counts are higher in newborns than in adults but they do not display striking differences in phenotype, except for an increased frequency of expression of the inhibitory CD94/NKG2A receptor. They display some inherent functional defects, mainly a lower cytolytic capacity that may contribute to the immaturity of the neonatal immune system. Changes in circulating levels of NK cells observed during pediatric infections and the ability of NK cells from newborns and children to produce interferon-γ at the encounter with pathogens indicate that NK cells participate in the immune response to infectious diseases in early life. Unfortunately, information is currently insufficient to assess whether these NK cell responses really contribute to control infections, either vertically transmitted or acquired in infancy.

Evaluation of cytotoxic function and apoptosis in interleukin (IL)-12/IL-15-treated umbilical cord or adult peripheral blood natural killer cells by a propidium-iodide based flow cytometry

Both deficient natural killer (NK) cell effector function and increased propensity to apoptosis of neonatal NK cells contribute to the increased susceptibility to infection in the neonates. Interleukin (IL)-12 and IL-15 are two immunoregulatory cytokines known to enhance cytolytic function of neonatal NK cells. The present study aims to simultaneously investigate the effect of IL-12/IL-15 on K562 cytotoxicity as well as NK cells apoptosis of enriched umbilical cord blood (CB) and adult peripheral blood (APB) NK cells, using flow cytometric cytotoxicity assays. The results indicated that (i) prior to cytotoxicity assays, CB NK cells underwent greater degree of spontaneous apoptosis than did APB NK cells; (ii) both IL-12 and IL-15 inhibited the spontaneous apoptosis of CB NK cells, while IL-15 promoted the apoptosis in APB NK cells; (iii) the deficient K562 cytotoxicity of CB NK cells could be enhanced to levels comparable with that of APB NK cells by IL-15; (iv) IL-15 increased the percentages of apoptosis in NK-K562 conjugates in a dose-dependent manner in both CB and APB with a greater effect seen with APB NK cells; (v) target-induced apoptosis was observed with APB NK cells which were further enhanced with IL-15. However, CB NK cells, unstimulated or IL-15-activated, were resistant to K562-induced apoptosis. Thus, the multi-parameter flow cytometry analysis not only demonstrates better for the deficient CB NK function but also provides greater details for cytotoxic mechanisms of NK cells.

Potentiation of tumor metastasis in adulthood by neonatal endotoxin exposure: sex differences

Previous research in rodents has demonstrated that neonatal exposure to bacterial endotoxin alters the hypothalamic-pituitary-adrenal (HPA) axis resulting in hypersecretion of corticosterone in response to stress in adulthood. Given the known interactions between glucocorticoids and the immune system we tested the hypothesis that such alterations may impact on immune outcomes. Male and female Fischer 344 neonate rats were treated with endotoxin (0.05 mg/kg lipopolysaccaride from Salmonella enteritidis) or vehicle on days 1, 3, 5 and 7 postpartum. In adulthood, animals were subjected to chronic stress and the effect on resistance to tumor colonization (Exp. 1), natural killer (NK) cell activity (Exp. 2), and HPA reactivity (Exp. 3) was assessed. Neonatal endotoxin treatment was found to significantly impair NK cell activity and decrease resistance to tumor colonization in male but not female rats (P<0.05). Neonatal endotoxin exposure did not affect corticosterone responses to chronic stress in male or female rats, but the corticosterone response to acute stress was potentiated by endotoxin exposure, most notably in females. In conclusion, neonatal endotoxin exposure was found to be associated with a sexually differentiated impairment in tumor colonization and NK activity and long-term alterations in corticosterone responses to stress. The effect on tumor colonization and NK activity was not, however, critically mediated by corticosterone levels. These findings suggest that neonatal bacterial infections may have long-term health implications, specifically in terms of resistance to cancer spread in adulthood.

Correlation of susceptibility of immature mice to fungal infection (blastomycosis) and effector cell function

Immature mice are highly susceptible to blastomycosis, which is similar to other mycoses and has parallels in humans. The murine susceptibility is noteworthy in that it persists beyond the development of resistance to other, nonfungal pathogens and the maturation of most immune functions. As the susceptibility to blastomycosis appeared to be related to an early event after infection, primary effector cell function was studied. We found that peritoneal inflammatory cells, enriched for neutrophils, from immature (3-week-old) mice killed nonphagocytizable Blastomyces dermatitidis cells less (25%) than did cells from mature (8-week) mice (70%) (P<0.01), a defect intrinsic to the neutrophils. This correlated with an impaired immature cell oxidative burst. Killing of phagocytizable Candida albicans was not significantly different, 73 versus 87%. Thioglycolate-elicited cells were more impaired; killing of B. dermatitidis was insignificant, and killing of C. albicans was more impaired in immature (16% killing) than in mature (45%) cells (P<0.02). Peripheral blood neutrophils from mature animals killed B. dermatitidis (41%) more than did those from immature animals (10%) (P<0.02); C. albicans was killed efficiently by both. Resting or activated peritoneal macrophages from both types of animals showed no differences in B. dermatitidis killing. These results suggest that the susceptibility of immature mice is related at least in part to the depressed capacity of their neutrophils to kill B. dermatitidis.

Can cord blood cells support the cytokine storm in GvHD?

Cord blood has a high number of proliferating hematopoietic progenitors and is therefore used as an alternative source of hematopoietic cells for allogeneic transplantation. In addition there is a wider availability of cord blood and a lower cost of procurement compared to bone marrow. However one of the most interesting immunological benefits of a cord blood transplant that has been proposed is the low severity of Graft versus Host Disease (GvHD). This review aims to address some of the immunological reasons why this may be the case by assessing the role of cord blood cytokines in the cytokine storm of GvHD.

Reversal of human immunodeficiency virus type 1 protein-induced inhibition of natural killer cell activity by alpha interferon and interleukin-2

A recombinant fusion peptide, Env-Gag, derived from the human immunodeficiency virus type 1 (HIV-1) genome corresponding to a defined portion of the envelope (Env) and internal core (Gag) proteins was examined for immunoregulatory effects on the cytotoxic activity of natural killer (NK) cell-enriched, large granular lymphocytes (LGL) from healthy donors. Percoll-separated, NK cell-enriched LGL precultured for 24 h with Env-Gag at 10- and 50-ng/ml concentrations, which significantly stimulated lymphocyte proliferation, caused significant suppression of NK cell activity. Denatured Env-Gag did not cause any effect on the NK cell activity of LGL. Two other control peptides, one derived from the Escherichia coli vector used to clone the HIV Env-Gag fusion peptide and the other derived from a non-HIV-1 viral antigen (rubeola virus), did not produce any observable effect on the NK cell activity of LGL, demonstrating the specificity of the effect produced by Env-Gag. Subsequent treatment of LGL with alpha interferon (IFN-alpha) or interleukin 2 (IL-2) alone partially reversed the Env-Gag-induced suppression of NK cell activity. However, LGL treated with both IFN-alpha and IL-2 completely reversed the suppression of NK cell cytotoxicity by Env-Gag. The combined effect of IFN-alpha and IL-2 in enhancing NK cell activity may provide a novel therapeutic approach to the restoration of depressed NK cell activity observed in HIV-infected patients.

Adhesion defects of antibody-mediated target cell binding of neonatal natural killer cells

Neonates are unusually susceptible to herpes simplex virus infection, which may be explained in part by defects in killing of herpes simplex virus-infected cells by natural killer (NK) cell cytotoxicity and antibody-dependent cellular cytotoxicity. The mechanism for these defects remains poorly defined. We have for the first time used immunomagnetically enriched NK cells to explore neonatal NK cell phenotype and target cell adhesion. CD56-positive neonatal NK cells had markedly lower CD57 expression, but adult level expression of adhesive glycoproteins (CD18, CD44) and Fc receptor for IgG (CD16). Although the cells conjugated normally with target cells in the absence of antibody, antibody-mediated conjugation was significantly lower than that of NK cells from adults (p < 0.002). These results demonstrate intact adhesion in neonatal NK cell cytotoxicity. In contrast, defective neonatal antibody-dependent cellular cytotoxicity is caused, in part, by an adhesion defect in the presence of antibody.

Interleukin (IL)-15 enhances antibody-dependent cellular cytotoxicity and natural killer activity in neonatal cells

Interleukin (IL)-15 is a novel cytokine that is very similar to IL-2 in receptor specificity and biological activities. We compared the ability of IL-15 and IL-12 to enhance the cytotoxicity of neonatal (cord blood) and adult mononuclear cells (MNC) in both natural killer (NK) and antibody-dependent cellular cytotoxicity (ADCC) assays. Incubation with IL-15 (10 ng/ml) or IL-12 (1 ng/ml) for 18 h enhanced the NK activity (using K562 target cells) of both cord and adult MNC, increasing cord cell cytotoxicity threefold. Similar enhancement was seen in ADCC assays using erythrocyte targets and NK-resistant CEM cells coated with HIV gp-120 antigen. Incubation of cord cells with IL-15 or IL-12 for 1 week increased both NK and ADCC, although the combination produced less of an effect than either cytokine alone. IL-15 also increased the percentage of CD16+/CD56+ cells after 1 week incubation. This enhancement of NK and ADCC activities and the number of NK cells by IL-15 suggests it may be clinically useful in treating immunodeficient patients.

Cord blood CD16+56- cells with low lytic activity are possible precursors of mature natural killer cells

Human natural killer (NK) cells are defined as being membrane CD3-, CD16+, and/or CD56+ lymphocytes; however, little is known about the ontogenic development and maturational pathways of human NK cells. The functional, phenotypic, and maturational characteristics of human umbilical cord blood (CB) NK cell subsets were studied to gain insight into the ontogenic and maturational pathways of human NK cells. We have previously shown that there is a novel subset of CD16+ CD56- NK cells present in CB. Here we further demonstrate differences in the expression of the NK-associated molecules CD2, CD7, CD8, and CD25 between CB and peripheral blood (PB) NK cells and between CB NK cell subsets. Although CB NK cell subsets were deficient in or had less lytic activity against K562 cells compared to PB NK cells, CB NK cells did possess the lytic molecules perforin and granzyme B and when artificially stimulated to secrete their granules during lytic assays, were capable of lytic activity equivalent to that of PB NK cells. Regardless of differences in phenotype and function of CB NK cell subsets, short-term and long-term incubation with cytokines induced functional (adult-like NK activity) and phenotypic (adult-like CD16+56+ or CD16-56+ surface antigen phenotype) maturation, respectively. Interleukin-2 (IL-2), IL-12, and IL-15, but not IL-7, interferon-gamma (IFN-gamma) nor tumor necrosis factor-alpha (TNF-alpha) induced functional and phenotypic maturation of CB NK cell subsets. Interestingly, culture of CB NK cell subsets with IL-2 or IL-15 led to acquisition of predominantly a CD16+56+ phenotype, while culture with IL-12 led to acquisition of both CD16+56+ and CD16-56+ phenotypes. Both functional and phenotypic maturation were not dependent upon proliferation. Studies using neutralizing anti-IFN-gamma and anti-TNF-alpha antibodies showed that survival and phenotypic maturation upon cytokine stimulation is influenced by endogenous production of TNF-alpha but not IFN-gamma. These results demonstrate that CB NK cell subsets are functionally and phenotypically immature but are capable of maturation. Additionally, CD16+56- NK cells are implicated as possible precursors of mature CD16+56+ and CD16-56+ NK cells.

Characterization of natural killer and antibody-dependent cellular cytotoxicity of preterm infants against human immunodeficiency virus-infected cells

The odds risk of vertical transmission of human immunodeficiency virus (HIV) to preterm infants is almost four times that of term infants and may relate to maternal and neonatal factors. We characterized the competence of early nonspecific cellular immunity, namely natural killer cytotoxicity (NKC) and antibody-dependent cellular cytotoxicity (ADCC), of peripheral blood mononuclear cells (PBMC) from preterm (n = 20) and term neonates (n = 28) versus adult controls against a T cell line infected with the human T cell lymphotrophic virus-III(B) using a chromium-51 release assay. PBMC from term neonates exhibited levels of NKC activity equal to adults against HIV-infected targets, yet the NKC capacity of preterm neonatal PBMC was significantly diminished. The ADCC activity of both term and preterm neonatal PBMC against HIV-infected targets was significantly less than that of adult PBMC. Overnight stimulation of a subset of samples with IL-12 augmented the NKC activity of both infant groups and adults, whereas the ADCC activity remained unchanged. These findings demonstrate that term neonates are deficient in ADCC against HIV-infected targets, whereas preterm infants are deficient in both NKC and ADCC, which may relate, in part, to the increased risk of transmission of HIV with preterm delivery. In addition, IL-12 has the potential to augment both term and preterm neonatal antiviral defense.

Development of immune functions related to allergic mechanisms in young children

The newborn immune system differs quantitatively and functionally from that of adults. Development of the immune system has important implications for childhood diseases. The immaturity of the immune system in the first years of life may contribute to failure of tolerance induction and in the development of allergic disease. T cell function is diminished, especially the capacity to produce cytokines; production of interferon (IFN)-gamma, and IL-4 is strongly reduced. IFN-gamma has been found to be even lower in cord blood of newborns with a family history of atopy. Differences in other cell types (natural killer cells, antigen-presenting cells, and B cells) could also play a role in the development of allergic disease. Current data suggest that irregularities in IgE synthesis, helper T cell subsets (Th1, Th2, CD45RA, and CD45RO), cytokines (IL-4, IFN-gamma), and possibly other cell types may play a role in the development of allergy in childhood. Moreover, the role of cell surface molecules, like co-stimulatory molecules (CD28, CD40L), activation markers (CD25), and adhesion molecules (LFA-1/ICAM-1, VLA-4/ VCAM-1) is also discussed. These variables are modulated by genetic (relevant loci are identified on chromosome 5q, 11q, and 14) and environmental forces (allergen exposure, viral infections, and smoke). The low sensitivity of current predictive factors for the development of allergic diseases, such as cord blood IgE levels, improves in combination with family history and by measurement of in vitro responses of lymphocytes and skin reactivity to allergens. New therapeutic approaches are being considered on the basis of our current understanding of the immunopathology of allergic disease, for instance cytokine therapy and vaccination with tolerizing doses of allergen or peptides.

Effect of age and route of inoculation on outcome of neonatal herpes simplex virus infection in guinea pigs

The morbidity and mortality of neonatal herpes simplex virus infection remains unacceptably high despite antiviral therapy. A better understanding of factors that might contribute to this poor outcome is needed but has been hindered by a lack of a good animal model. The recently described guinea pig model of neonatal HSV-2 infection was used to explore the effect of age and route of inoculation on the outcome of infection. After intranasal inoculation the onset, extent, and severity of the primary disease, as well as the number of recurrent lesion days, varied inversely with age. The route of inoculation also affected the outcome. Newborn animals were inoculated either intradermally on the scalp or by the intranasal, oral or corneal route. Animals inoculated on the scalp had the best outcome with no deaths or evidence of neurologic disease while the intranasal route produced the most severe disease, 88% mortality. Neurologic disease was common after oral (41%) and corneal (56%) inoculation but resolved spontaneously whereas following intranasal (39%) inoculation all animals with neurologic disease died. Recurrent disease manifest by cutaneous lesions was observed in all survivors of each group but also differed by the route of inoculation. The guinea pig model of neonatal HSV-2 disease appears to mimic human disease. The studies presented here show that the outcome of infection is influenced by the age and route of inoculation.

The development of sexual dimorphism in natural killer cell activity and resistance to tumor metastasis in the Fischer 344 rat

The development of sexual dimorphism in the number and activity level of natural killer (NK) cells was studied in the inbred Fischer 344 rat from prepubescence to maturity. Additionally, in view of the biological significance of NK cells in controlling cancer, especially the metastatic process, we used a syngeneic mammary tumor (MADB106) to assess the host anti-metastatic activity. This tumor model was used because NK cells control the lung clearance of i.v.-injected MADB106 tumor cells, a process that critically affects the metastatic colonization of these tumor cells in the lungs. The results indicated that although prepubescent (36 days of age) males and females exhibited greater NK cytotoxicity (assessed in vitro) and higher anti-metastatic activity, evidenced by fewer tumor cells retained in the lungs. On the other hand, the mature males (140-170 days of age) displayed greater LGL/NK number and activity per ml blood, retained fewer tumor cells, and developed fewer lung tumor colonies compared to the females. During early postpubescence (63 days of age), a transitional stage between prepubescence and maturity, females and males exhibited equivalent numbers of circulating LGL/NK cells, and females displayed slightly greater NK cytotoxicity per ml blood yet retained somewhat greater numbers of tumor cells compared to the males. Overall, whereas the males exhibited increasing levels of NK number and activity throughout the age span tested, the females, despite displaying greater NK function compared to the males at prepubescence and slight improvement at postpubescence, fell behind the males in these indices of NK function at maturity.

Selective inhibitory effects of stress hormones on natural killer (NK) cell activity of lymphocytes from AIDS patients

To examine the potential role of stress hormones in the progression of HIV infections, we developed an in vitro model system that investigates the effects of cortisol, adrenocorticotropin-releasing hormone (ACTH) and beta-endorphin on the natural killer cell activity of lymphocytes from normal subjects and AIDS patients. The system employs a 4 hr 51Cr release assay and K562 target cells. Direct addition of cortisol (0.05, 0.1, and 0.2 microgram/ml) or ACTH (10(-6) to 10(-8) M) to the mixture of effector and prelabeled target cells did not produce any significant immunoregulatory effects on the NK cell activity of normal lymphocytes. Direct addition of beta-endorphin (10(-13) to 10(-17) M) to the mixture of effector and prelabeled target cells did not produce any significant immunoregulatory effects on the NK cell activity of lymphocytes from normal or AIDS subjects. However, cortisol and ACTH significantly inhibited the NK activity of lymphocytes from AIDS patients. The selective inhibitory effects of cortisol and ACTH in patients with HIV infections are consistent with a model which proposes that stress related neurohormones and/or neuropeptides may be involved in the progression of HIV infections.

Differential effects of human immunodeficiency virus type 1 envelope protein gp120 on interferon production by mononuclear cells from adults and neonates

While considerable progress in examining the course of human immunodeficiency virus (HIV) infection in adults has been made, a better understanding of the natural history of perinatal HIV infection remains to be obtained. Dysregulation of the production and functions of various cytokines, especially the interferons (IFNs), during HIV infections has been reported. Using an in vitro model system, we examined the effects of the HIV type 1 envelope protein, gp120 (10, 50, and 100 ng/ml), on gamma IFN (IFN-gamma) and IFN-alpha production by lymphocytes from neonates and adults and also examined the potential regulatory effects of gp120 on phorbol 12-myristate acetate (PMA)- and Sendai virus-induced IFN-gamma and IFN-alpha production by lymphocytes. PMA at a concentration of 50 ng/ml plus 50 ng of calcium ionophore A23187 per ml was used to induce IFN-gamma, while 150 hemagglutinating units of Sendai virus was used to induce IFN-alpha production. The antiviral activity of both IFN-alpha and IFN-gamma in leukocyte culture supernatants was assayed on BG-9 cells by a dye uptake technique using vesicular stomatitis virus as a challenge virus. Placental cord blood leukocyte (CBL) samples from healthy, term infants and adult peripheral blood leukocytes (APBL) produced no IFN in response to gp120. However, CBL produced significantly decreased levels of IFN-gamma compared with APBL in response to PMA plus ionophore. gp120 significantly suppressed both Sendai virus-induced IFN-alpha and PMA-induced IFN-gamma production by both CBL and APBL in a dose-dependent manner. However, gp120-induced suppression of IFN-alpha and IFN-gamma was significantly greater with CBL than with APBL. Treatment of CBL and APBL with gp120 did not induce any phenotypic alteration of the CD45 RO+ subset. Increased suppression of IFN-alpha and IFN-gamma production by gp120 in neonates may partially explain their apparent increased susceptibility to the clinical progression of HIV infections compared with that of adults.

Cord blood natural killer cells are functionally and phenotypically immature but readily respond to interleukin-2 and interleukin-12

Human umbilical cord blood (CB) is being increasingly used both as an alternative to bone marrow to transplant children and for experimental insight into the ontogenic and maturational characteristics of blood cells. We studied the functional and phenotypic characteristics of CB natural killer (NK) cells because of the possibly important role such cells may play in a transplant setting and to gain insight into the little known ontogenic differences and maturational pathways of NK cells. It was found that CB NK lytic activity is usually deficient and that this deficiency cannot be fully explained by the presence of insufficient percentages of CD56+ cells. Although CD16+CD56+ and CD16-CD56+ NK cell subsets typical of adult peripheral blood (PB) are present, a significant population of CD16+CD56- cells also exists in CB. CB CD16+CD56- cells have little or no lytic capabilities; CB CD16+CD56+ cells vary in their lytic capabilities. Although a decreased ability to bind target cells may contribute to the deficient lytic activity of these CB NK cell subsets, studies suggest that other factors must also play a role. Short-term incubation with interleukin-2 (IL-2) or interleukin-12 (IL-12) substantially increases the lytic capabilities of CB NK cells, and long-term incubations induce lymphokine-activated killer (LAK) cell generation. Cell depletion experiments show that activated CD56+ NK cells are responsible for the lytic activity of CB LAK cells. Flow cytometric analysis reveals that during LAK cell generation, CB undergoes phenotypic changes similar to those of PB except that CD16+CD56- cells are still present.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective inhibition by alcohol and cortisol of natural killer cell activity of lymphocytes from cord blood

1. The immunosuppressive effects of drugs such as alcohol or hormones such as cortisol may be age-related. To test this hypothesis, the authors investigated the in vitro effects of ethanol (EtOH) and cortisol on Natural Killer (NK) cell activity of lymphocytes from normal cord blood in comparison with that of lymphocytes from normal adult peripheral blood. 2. K562, an erythroleukemia cell line, was used as a target in a 4 hr 51Cr release assay. 3. Ethanol at 0.3% (V/V) and cortisol at 0.05, 0.1 and 0.2 microgram/ml concentrations, added directly to a mixture of effector and target cells significantly suppressed the NK activity of cord blood lymphocytes in a dose dependent fashion, whereas similar concentrations of either EtOH or cortisol did not manifest significant immunoregulatory effects on NK cell activity of normal adult lymphocytes. 4. Pre-treatment of the target with either EtOH or cortisol for 4 hours did not affect cytotoxicity. Inhibition of cytotoxicity was also not due to direct toxicity of effector cells because lymphocytes treated with either EtOH or cortisol showed normal 51Cr release and their viability was comparable to that of untreated control cells. 5. This suggests a selective inhibitory effect of EtOH and cortisol on NK activity of neonatal lymphocytes that may be of clinical significance.

Modulation of the cell-mediated immune function by interferon alpha, beta or gamma can partially reverse the immunosuppression induced by human T-cell leukemia virus I in human cord blood cultures

Infection with human T-cell leukemia virus type I (HTLV-I) is associated in vitro and in vivo with a remarkable depression of cell-mediated immune functions. In the present report it is shown that early events following virus-induced suppression of the cell-mediated immune response of freshly isolated cord blood mononuclear cells (CBL) infected with HTLV-I can be partially counteracted by treatment with interferons alpha, beta or gamma (IFN). All three types of IFN exerted a protective effect on CBL cultures exposed to the virus. This resulted in: (a) a reduced number of virus-positive cells until 4 weeks of culture; (b) delay in the clonal expansion of infected cells (IFN alpha and gamma); (c) increased natural killer cell activity of CBL, 1 week post-infection (p.i.), mediated by IFN gamma; (d) increase of allospecific recognition of infecting and priming HTLV-I donor MT-2 cells by CBL in a cytotoxic-T-lymphocyte-like response, mediated by IFN and particularly by IFN gamma; (e) phenotype distribution of CBL subpopulations, tested 4 days p.i., more similar to that of non-infected CBL cultures. In contrast, the overall CBL proliferation, that is profoundly depressed during the first week p.i., was not restored by IFN treatments, suggesting that boosting of the cell-mediated killing induced by IFN might involve the maturation of undifferentiated precursor cells rather than stimulation of their proliferation. The improvement of the efficiency of the antiviral immune response induced by treatment with IFN is likely to contribute to the clearance of virus-positive cells during the early phase of infection. This would provide experimental evidence to support an immunopharmacological approach contributing to the conversion of HTLV-I carriers from positive to negative.

Immunoregulation of lymphokine-activated killer cells

The in vitro effects of Concanavalin A (Con A) and prednisolone (PRD) on the cytotoxic functions of lymphocytes and the generation of lymphokine-activated killer (LAK) cells were investigated. Con A at concentrations ranging from 1 to 40 micrograms/ml did not significantly affect the cytotoxicity of LAK cells when added directly to the effector and target cell mixture in a 4-hr 51Cr release assay. The generation and lytic capacity of LAK cells were significantly affected by Con A in a dose-dependent manner when lectin was added at the initiation of culture. Suppression of LAK cell activity was demonstrable at effector: target (E:T) cell ratios. Lymphocyte cultures incubated with PRD at concentrations ranging from 10(-9) to 10(-4) M showed a decrease in both the numbers of and activity of LAK cells using a variety of target cells. Pretreatment of target cells with either PRD or Con A did not affect their sensitivity to lysis by LAK cells and incubation of lymphocytes with Con A did not induce autoreactive cytotoxic or suppressor cells directed against LAK cell activity. Thus while PRD and Con A can inhibit the generation of LAK cells, they also directly inhibit their specific cytotoxic activity on a per cell basis. These results suggest that like other cytotoxic cells, LAK cells are also under active immunologic control.

The effect of age of cattle on the in vitro production of interferon by peripheral blood mononuclear cells

Peripheral blood mononuclear cells (PBMC) from normal cattle of different ages and from specific pathogen-free (SPF) calves, 2 to 4 weeks old, were cultured with bovine herpes virus type 1 (BHV1), parainfluenza-3 virus (PI3) and phytohaemagglutinin (PHA). The interferon (IFN) produced was characterized by acid stability and neutralizing antisera to recombinant bovine interferons. The virus preparations were presented either live or inactivated and as cell-bound virus or free virions. PBMC from cattle of all ages produced IFN-alpha when stimulated with live BHV1 and PI3 viruses. IFN-alpha was also produced with inactivated BHV1, even in cell cultures from SPF calves. However, inactivated PI3 virus failed to induce IFN in PBMC cultures from normal cattle, but approximately half of the animals, mostly calves, produced IFN-gamma spontaneously in 48 h cultures in the absence of added antigen. PHA induced IFN-gamma at an optimal concentration of 20 micrograms per ml after 3 days in culture. An age-related maturation of the IFN response was observed as PBMC from calves less than 2 weeks old produced little or no IFN when induced with either PHA or inactivated BHV1, although some IFN-alpha was produced in cultures containing live virus. Both adherent and non-adherent cells from adults and calves over 2 weeks old produced IFN on induction with inactivated BHV1 but only the non-adherent cell population produced IFN spontaneously or in response to inactivated PI3.

Depression of early phase of HTLV-I infection in vitro mediated by human beta-interferon

Natural human interferon beta (beta-IFN) was tested during the early phase of in vitro infection with HTLV-I virus of human cord blood mononuclear cells (CBL), to evaluate whether its antiviral and immunomodulating effects might prevent spreading of infection in the host. beta-IFN was found to reduce HTLV-I transmission and integration in CBL cultures. Moreover, beta-IFN had no effect in preventing virus transmission and integration in K562 and a very limited effect in HL60 and Molt-4 human tumour lines, suggesting a cell-type specific mode of action. beta-IFN induced a 'priming' response on CBL, since overnight pretreatment of recipient cells or one single treatment at the onset of the coculture were almost equally effective in protecting against HTLV-I infection. During the early days post infection (p.i.), IFN-treated CBL showed a pattern of phenotypic markers that was closer to that of non-infected CBL. In contrast, untreated CBL exposed to HTLV-I showed a percent increase of Tac+, M3+ and Leu 11+ subpopulations. Cell-mediated immune responses of CBL were depressed after coculturing with HTLV-I producer MT-2 cells. beta-IFN was able to boost the cell-mediated cytotoxicity of fresh and infected CBL against both K562 and MT-2 target cells. Leukocyte blastogenesis in mixed lymphocyte/tumour cell cultures, evaluated in terms of 3H-thymidine incorporation during the first week p.i., was also enhanced by IFN when macrophages and lymphocytes were reconstituted at an optimal 1:20 ratio. It is conceivable that this overall enhancement of the immune response induced by beta-IFN could contribute to reduce HTLV-I infection in vitro.

Activation of natural killer cells in newborn piglets by interferon induction

Natural killer (NK) cell activity in the peripheral blood lymphocytes (PBL) of newborn piglets, normally negligible, was stimulated by in vitro treatment with porcine type I interferon (IFN), and the NK activity of PBL from weaned piglets was augmented by the same treatment. Binding of the PBL to the PK-15 targets used in the single cell cytotoxicity assay for NK activity was not affected by age or by IFN treatment. When newborn piglets were treated with a single intravenous dose at 2 days of age of 0.5 mg/kg of polyinosinic:polycytidylic acid complexed with poly-L-lysine and carboxymethylcellulose (poly ICLC), a synthetic IFN inducer, their IFN levels peaked at 6 h post-induction, and NK activity in their PBL peaked at 24 h post-induction at the level normally found in weaned piglets. The NK activity then declined until 7 days post-induction, when it increased again in a similar manner to that in untreated control piglets. Target-binding of the PBL was not affected by poly ICLC treatment of the piglets. Newborn piglets treated with poly ICLC and subsequently exposed to infection with transmissible gastroenteritis (TGE) virus showed a delay in onset of clinical signs of TGE compared with untreated control piglets. It was concluded that NK cells in newborn piglets can be activated by treatment of the piglets with poly ICLC, and that the presence of active NK cells is associated with some increase in resistance to challenge with TGE virus.

Enhancement of natural killer cell activity and interferon production by manganese in young mice

The effect that MnCl2 has on murine splenic natural killer (NK) cell activity was investigated in infant (10 days old), pre-weanling (18 days old) and weanling (24 days old) C57BL/6J mice. A single intraperitoneal injection of 10, 20 or 40 micrograms MnCl2/g body weight caused a significant enhancement in NK activity, as determined by the in vitro 51Cr release assay. Comparable enhancement of NK activity was observed for age-matched mice injected intraperitoneally with polyinosinic polycytidylic acid (Poly I:C). Both MnCl2 and Poly I:C caused elevations in serum interferon levels. Time-course studies revealed that interferon levels returned to normal within 48 hours following injection with either MnCl2 or Poly I:C; however enhanced NK activity persisted for up to 48 hours in Poly I:C-injected mice and 72 hours in MnCl2-injected mice. The administration of rabbit anti-asialo GMl to MnCl2-injected mice completely abrogated the enhanced NK activity. In addition, the injection of rabbit anti-mouse interferon alpha, beta but not gamma completely abrogated the enhanced NK activity. In addition, the injection of rabbit anti-mouse interferon alpha, beta but not gamma completely abrogated the enhancement of NK activity by MnCl2 and to a lesser extent the enhancement of NK activity by Poly I:C. These results indicate that despite low levels of NK activity in pre-weanling mice, MnCl2 is capable of enhancing this activity by 8-9 fold. Furthermore, Mn-enhanced NK activity in these young mice appears to be mediated by the production of interferon alpha, beta.

Deficiency of inducible suppressor cell activity in the Chediak-Higashi syndrome

Peripheral blood lymphocytes from two Chediak-Higashi syndrome (CHS) patients were examined for their 1) natural killer (NK) cell functions 2) concanavalin A (Con A)-inducible suppressor cell activity, 3) soluble suppressor factor production, and 4) responsiveness to interferon alpha and interleukin-2 in comparison with age-matched normal controls. Peripheral blood lymphocytes or NK-enriched large granular lymphocytes from Chediak-Higashi syndrome patients showed negligible cytotoxic activity against several target cells. Although the NK activity of Chediak-Higashi syndrome lymphocytes could not be restored to normal levels by treatment with either interferon or interleukin-2, the percent enhancement of NK activity was higher for the patients than the controls. Soluble suppressor factor activity of culture supernates from the lymphocytes of Chediak-Higashi syndrome patients significantly inhibited the NK activity of allogeneic, normal peripheral blood lymphocytes, whereas lymphocytes from Chediak-Higashi syndrome patients precultured with Con A failed to suppress the cytotoxic activity of normal lymphocytes. These results demonstrate a previously unrecognized suppressor cell dysfunction in CHS patients.

Cytotoxic studies in human newborns: lessened allogeneic cell-induced (augmented) cytotoxicity but strong lymphokine-activated cytotoxicity of cord mononuclear cells

Nonspecific cytotoxic responses such as natural killer activity can be increased in vitro by incubating effector cells with soluble factors or allogeneic cells. We sought to determine if newborn cells, known to be deficient in most cytotoxic responses, including resting NK activity, could develop enhanced cytotoxic responses following incubation with allogeneic cells (augmented cytotoxicity) or with lymphokines (lymphokine-activated cytotoxicity). Cord whole mononuclear cells (WMC) incubated with irradiated Raji cells for 5 days develop lower levels of cytotoxicity toward K562 targets at both a 20:1 effector:target (E:T) ratio (39 +/- 2.7% vs 49 +/- 3.6%) and a 10:1 E:T ratio (29 +/- 2.6% vs 40 +/- 3.6%) than do adult cells. Lessened specific cytotoxicity of cord cells developed toward the sensitizing Raji cells was also observed at both E:T ratios. Attempts to enhance the induced cytotoxicity by incubation with interferon or isoprinosine were unsuccessful. In contrast, lymphokine (i.e., interleukin 2)-activated killer (LAK) cytotoxicity is not deficient in cord WMC. Indeed, the level of LAK cytotoxicity is equivalent to that observed with similarly treated adult cells despite a lower baseline level of cytotoxicity toward the target cells. In the presence of purified IL-2 for 5 days, cord WMC cytotoxicity against K562 cells increased from 12 +/- 2.6 to 71 +/- 4.2% and against Raji cells increased from 9.6 +/- 2.5 to 48 +/- 6.7%. Similarly treated adult cells increased their killing against K562 from 23 +/- 4.2 to 61 +/- 4.5% and against Raji from 12 +/- 3.0 to 36 +/- 5.3%. This substantial lymphokine-activated cytotoxicity of newborn cells suggests the possibility of therapeutic intervention with purified lymphokines in neonatal infections or neoplasms.

Immunoregulatory dysfunctions in type I diabetes: natural and antibody-dependent cellular cytotoxic activities

Peripheral blood lymphocytes from 13 patients with established insulin-dependent diabetes mellitus (IDDM) and 2 prediabetic patients were examined for natural killer (NK) and antibody-dependent cellular cytotoxic activities (ADCC), lectin-dependent cellular cytotoxicity (LDCC), interferon- and interleukin-2-induced cytotoxicity, and concanavalin A-induced suppressor-cell activities in comparison with age-matched normal controls. IDDM patients demonstrated normal levels of NK and ADCC activities against K562 and antibody-coated SB target cells, respectively, compared to controls. IDDM patients showed normal levels of LDCC activity. Notable deviations from control values were, however, observed with diabetic lymphocytes in the following systems. Interferon- and interleukin-2-induced NK activities were significantly higher with IDDM lymphocytes than with control cells. IDDM lymphocytes precultured with concanavalin A demonstrated lower NK and ADCC activities than control cells and manifested decreased suppressor effects on the NK activity of normal allogeneic lymphocytes. Lymphocytes from one of two prediabetic patients showed increased NK, ADCC, and LDCC activities in comparison to controls. The increased interferon- and interleukin-2-induced enhancement of NK activity and reduced suppressor activity of lymphocytes from IDDM patients may be involved in the pathogenesis of the disease.