Subpopulations of B cells in germinal centers. III. HJ6, a monoclonal antibody, binds globoside and a subpopulation of germinal center B cells

To identify surface Ag uniquely expressed on human germinal center B cells, we produced a mouse mAb, HJ6. When tonsillar lymphocytes were examined, HJ6 did not label T cells and labeled only about half of PNA+ B cells that were HK23-. HJ6 did not label mononuclear cells from peripheral blood, splenocytes, and any of 29 cell lines including 23 B cell lines. This binding pattern of HJ6 was very similar to that of a mAb named 5B5. It was shown previously that 5B5 bound a glycolipid named CTH (CD77) and its Ag was expressed on HK23- PNA+ tonsillar lymphocytes and Burkitt's lymphoma cell lines. Despite the similarity, HJ6 differed from 5B5: HJ6 did not stain Burkitt's lymphoma cell lines and stained PNA+ tonsillar lymphocytes in the presence of a large concentration of galactose. When its binding to isolated glycolipids was studied, HJ6 was found to bind globoside and Forssman Ag and not to other glycolipids including CTH. When its binding to neutral glycolipids extracted from tonsillar lymphocytes was studied, HJ6 bound only globoside; Forssman Ag was not detected in tonsillar lymphocytes. Taken together, we conclude that globoside is a B cell Ag expressed on a subpopulation of germinal center B cells.

Germinal center T cells are distinct helper-inducer T cells

Germinal centers (GCs) contain a significant number of CD4+ T cells, but what role these T cells may play in the development of GC B cells has not been determined. To gain insight into their role, we studied the phenotype of GC T cells and the lymphokines secreted by GC T cells isolated from human tonsils obtained after tonsillectomies. In addition to confirming that a large fraction of GC T cells are Leu-7(CD57)+ and Leu-8-, we found that they have no binding sites for peanut agglutinin. Furthermore, we found that they are CD45RA- and CD45R0+, the phenotype of helper-inducer T cells. We also found that Leu-7(CD57)+ cells display CD69, a phenotypic marker of very early cell activation, but do not display three other markers of cell activation: CD25 [interleukin-2 (IL-2) receptor], CD71 (transferrin receptor), and DR. When isolated, Leu-7(CD57)+ cells were stimulated in vitro with a mitogen that can induce peripheral blood T cells with the helper-inducer phenotype to produce various cytokines, Leu-7(CD57)+ cells did not produce IL-2, interleukin-4 (IL-4), interferon-gamma (IFN-gamma) or tumor necrosis factor-alpha (TNF-alpha) in significant amounts. Taken together, GC T cells from a distinct subpopulation of T cells with helper-inducer phenotype by their histologic location, by their surface phenotype, and by their ability to produce lymphokines. This finding is consistent with the possibility that GC T cells have been selectively recruited to actively help B cells develop in GCs.

Cytokine production by T helper cell subpopulations during prolonged in vitro stimulation

In man, CD4+ T cells can be divided into phenotypically distinguishable subsets with different function whereas CD4+ T cells with the opposite pheno-CD45RO and low levels of CD45RA antigen provide help for mitogen-induced immunoglobulin production whereas CD4+ cells with the opposite phenotype suppress immunoglobulin production. However, studies examining cytokine production by phenotypically defined CD4+ T cell subsets have led to different conclusions. Further, very few studies have examined cytokine production by freshly isolated CD4+ T cell subsets during extended culture periods. Thus, we examined the production of several cytokines (at various time points) by CD4+ T cell subsets that were isolated in several ways, and stimulated with PWM, Con A, and PHA in a well-defined serum-free culture system. We found that CD4+, CD45RA- (or CD45RO+) T cells consistently produced the most IL-2, IFN-gamma, and TNF-alpha after mitogen stimulation for 2 days. PWM induced the largest quantities of each cytokine, although a similar pattern of production was observed in response to Con A and PHA. We were unable to detect IL-4 production by mononuclear cells and CD4+ T cell subsets suggesting that, if it is produced at all, IL-4 is produced in extremely small quantities. When the culture period of initially CD45RO- T cells was extended beyond 2 days, the culture supernatant contained increased quantities of each cytokine and the cells in the culture had an increased number of cells expressing CD45RO antigen. Together, these data indicate that CD4, CD45RA- (or CD45RO+) T cells in peripheral blood are the major producers of IL-2, IFN-gamma, and TNF-alpha following short-term mitogen stimulation, and that phenotypically defined peripheral blood T cell subsets do not maintain a distinct pattern of cytokines during extended culture periods.

Bactericidal and opsonic activity of IgG1 and IgG2 anticapsular antibodies to Haemophilus influenzae type b

Complement-mediated bactericidal and opsonic activity of IgG1 and IgG2 antibodies to Haemophilus influenzae type b polysaccharide (polyribosyl ribitol phosphate [PRP]) were investigated. The antibody sources were IgG1 or IgG2 subclass polyclonal antibody fractions prepared by immunoabsorption of sera from adults immunized with PRP or PRP-diphtheria toxoid conjugate vaccine or clonally purified anti-PRP antibodies from eight adults immunized with PRP vaccine. In bactericidal assays using an inoculum of 3 x 10(3) colony-forming units (cfu)/ml, twofold lower concentrations of IgG1 compared with IgG2 antibody were required for 50% killing. With approximately 10(6) cfu/ml, IgG1 antibody killed 3 logs more of bacteria than were killed by comparable concentrations of IgG2 antibody. The IgG1 antibody also required lower concentrations of complement than did the IgG2 antibody for comparable bacteriolytic activity. Clonally purified IgG1 and IgG2 anti-PRP antibodies from most individuals showed similar relative differences in bactericidal activity. IgG1 anti-PRP antibody was also more efficient than IgG2 anti-PRP antibody in enhancing the uptake of radiolabeled type b H. influenzae by human polymorphonuclear leukocytes in the presence of complement and in protecting infant rats from developing bacteremia. However, the differences in opsonic or protective activity of the two subclasses were smaller than the differences in bactericidal activity. Thus, IgG1 anti-PRP antibody is functionally more effective than IgG2 antibody, but it is likely that both subclasses can confer protection against disease.

Immunologic and clinical status of blood donors with subnormal levels of IgG2

To determine the immunologic and clinical status of individuals from a general population with subnormal levels of IgG2, we prospectively studied 37 of 312 blood donors with low IgG2 levels identified among 8015 donors. We examined (1) G2m(23) allotypes, (2) levels of other IgG subclasses and immunoglobulin classes, (3) composition of peripheral leukocyte populations, (4) responses to two carbohydrate antigen vaccines, (5) in vitro secretion of IgG subclasses by isolated lymphocytes after mitogen stimulation, and (6) clinical histories. We found that most (90%) individuals with subnormal IgG2 levels had G2m(23)- allotypes, whereas only 30% of the unselected donors had G2m(23)-. When individuals were separated according to their G2m(23) allotype, we found that IgG2 "normal" range for individuals with G2m(23)- allotype is 35% lower than for individuals with G2m(23)+ allotype. Individuals who had G2m(23)- allotype and had IgG2 levels greater than or equal to 0.8 but less than 1.3 gm/L had no other immunologic abnormalities. In contrast, the individuals with G2m(23)+ allotype and with IgG2 levels less than 1.3 gm/L and the individuals with G2m(23)- allotype and with IgG2 levels less than 0.8 gm/L often had additional immunologic abnormalities, including IgA and/or IgG4 deficiency and decreased in vitro expression of IgG2 subclass. None of these individuals had a clinical history remarkable for recurrent infections. Thus, subnormal IgG2 levels interpreted with G2m(23) corrected normal ranges may be a marker of other immunologic abnormalities but taken alone probably have little clinical significance in a general healthy population.

Subnormal serum concentrations of IgG2 in children with frequent infections associated with varied patterns of immunologic dysfunction

To characterize more fully the immunologic basis for increased susceptibility to infection in patients with low serum concentrations of IgG2, we identified eight infection-prone children, 1 to 2 years of age, with serum IgG2 concentrations greater than 2 SD below the mean for age and followed their serologic and clinical courses for 1 to 3 years. Two of the eight children became clinically and immunologically normal and may have had transient IgG2 deficiency with an exaggerated developmental delay of this late-maturing subclass. The remaining six subjects had persistently subnormal or low-normal serum IgG2 levels and continued to experience frequent infections. All six of these children responded poorly to Haemophilus influenzae type b (Hib) polysaccharide, and four of six responded poorly to Streptococcus pneumoniae type 3 polysaccharide. Both IgG1 and IgG2-specific antibody responses to these vaccines were abnormal. Three of these six children also responded poorly to tetanus toxoid, an antigen that normally induces a predominant IgG1 response. Although five of these six children produced antibodies in response to Hib polysaccharide protein conjugate vaccine, three of four given Hib oligosaccharide CRM conjugate vaccine required booster doses to respond, a pattern of response characteristic of infants less than 6 months of age. Further, although serum concentrations of IgG1 were normal, peripheral blood mononuclear cells from four of six children tested produced extremely small amounts of IgG1 and IgG3 as well as IgG2. Finally, varied patterns of abnormalities of IgG, IgA, IgM, and IgG4 became apparent in five of the six children with persistently low serum IgG2 values. This study demonstrates that subnormal serum concentrations of IgG2 may be associated with varied patterns of immunologic dysfunction, some of which are evolving and may be responsible for increased susceptibility of these children to infection.

Clinical and immunologic characteristics of healthy children with subnormal serum concentrations of IgG2

To understand the relevance of subnormal serum concentrations of IgG2, we measured IgG2 in serum of 575 healthy children and identified 11 with concentrations greater than 2 SD less than the mean for age. The levels of IgG2 present were similar to those found in symptomatic children with IgG2 subclass deficiency associated with antibody deficiency. The 11 children ranged in age from 1 to 14 y (mean = 5.7). Detailed clinical information was available on 10 of the 11 children and each was matched for age with two controls. The median number of visits/y to the doctor for infectious illnesses was identical for the two groups (1.0). Nine of the children with subnormal IgG2 were followed for 1 to 5 y (mean = 2.3). All nine children had normal serum concentrations of IgA, IgG1, IgG3, and IgG4 but seven had persistently subnormal or low-normal serum IgG2 concentrations. One of these seven children also had a subnormal serum concentration of IgG, and one had subnormal IgM. Antibody responses to Haemophilus b polysaccharide vaccine were normal in five of six who were immunized. In vitro secretion of Ig by mitogen-stimulated peripheral blood mononuclear cells was measured in six of seven children with persistently subnormal or low-normal IgG2; five showed decreased secretion of IgG2, and two of the five also had subnormal secretion of IgG1 and IgG3. An important implication of this study is that the subnormal concentrations of serum IgG2 found in infection-prone children are not a sufficient explanation for their increased susceptibility to infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Clonal characterization of the human IgG antibody repertoire to Haemophilus influenzae type b polysaccharide. III. A single VKII gene and one of several JK genes are joined by an invariant arginine to form the most common L chain V region

To characterize the L chain V region repertoire of IgG anti-Haemophilus influenzae type b capsular polysaccharide (Hib-PS) antibodies, clonal antibodies were purified from immune serum and internal amino acid sequences of VKII anti-Hib-PS L chains obtained. We examined VKII L chains because it is the most common VL family expressed in the anti-Hib-PS response. Comparison of VKII amino acid sequences, including the entire CDR2 and CDR3 regions, of five anti-Hib-PS clonal antibodies from four unrelated individuals revealed complete identity with the exception of a single CDR3 residue from one antibody. When the sequence of these antibodies was compared with known VKII genes and myeloma proteins, it was found to be identical to the human VKII gene, A2, whose genomic sequence is presented here. In addition, all five of the VKII anti-Hib-PS antibodies examined contain an arginine inserted at the V-J junction. Finally, in contrast to the extraordinary homology of the VKII-encoded residues, there is variability in the JK gene utilization by these antibodies. These results demonstrate that the most common L chain V region in IgG anti-Hib-PS antibodies is the product of a single germ-line gene. The invariant arginine insertion suggests that this residue has an important role in Ag binding.

Clonal characterization of the human IgG antibody repertoire to Haemophilus influenzae type b polysaccharide. III. A single VKII gene and one of several JK genes are joined by an invariant arginine to form the most common L chain V region

To characterize the L chain V region repertoire of IgG anti-Haemophilus influenzae type b capsular polysaccharide (Hib-PS) antibodies, clonal antibodies were purified from immune serum and internal amino acid sequences of VKII anti-Hib-PS L chains obtained. We examined VKII L chains because it is the most common VL family expressed in the anti-Hib-PS response. Comparison of VKII amino acid sequences, including the entire CDR2 and CDR3 regions, of five anti-Hib-PS clonal antibodies from four unrelated individuals revealed complete identity with the exception of a single CDR3 residue from one antibody. When the sequence of these antibodies was compared with known VKII genes and myeloma proteins, it was found to be identical to the human VKII gene, A2, whose genomic sequence is presented here. In addition, all five of the VKII anti-Hib-PS antibodies examined contain an arginine inserted at the V-J junction. Finally, in contrast to the extraordinary homology of the VKII-encoded residues, there is variability in the JK gene utilization by these antibodies. These results demonstrate that the most common L chain V region in IgG anti-Hib-PS antibodies is the product of a single germ-line gene. The invariant arginine insertion suggests that this residue has an important role in Ag binding.

New fluorescence assay for the quantitation of fungi

Quantitative determination of fungal mass is easily achieved with a new procedure that detects particle epifluorescence. Fungi are detected after exposure to a fluorescent stain (Fungiqual; CIBA-GEIGY Corp., Summit, N.J.) by using a fluorescence particle concentration analyzer. This report describes a simple fluorescence method for quantitation of either yeast or mycelial forms of fungi. The nature of the staining reaction was studied, and a practical application of this procedure for determination of fungal susceptibility to an antifungal agent is presented.

Clonal characterization of the human IgG antibody repertoire to Haemophilus influenzae type b polysaccharide. II. IgG antibodies contain VH genes from a single VH family and VL genes from at least four VL families

To define the V gene family repertoire of human IgG anti-Haemophilus influenzae type b polysaccharide antibodies, we purified six IgG1 and nine IgG2 anti-Hib-PS antibodies to monoclonality from immune serum of six individuals and performed N-terminal amino acid sequence analysis. Of the 15 clonal antibodies we examined, all H chain V regions were of the VHIII family. In contrast, the L chains of these antibodies were clearly from at least four different VL families; VKI, VKII, VKIII, and V lambda. Interestingly. VL family expression correlated with the cross-reactivity of these antibodies to the capsular carbohydrate of Escherichia coli K100. VKII antibodies did not cross-react, whereas antibodies expressing V lambda, VKI, or VKIII generally cross-reacted. We conclude that L chain V regions are very important contributors to the limited heterogeneity in this antibody repertoire.

Clonal characterization of the human IgG antibody repertoire to Haemophilus influenzae type b polysaccharide. II. IgG antibodies contain VH genes from a single VH family and VL genes from at least four VL families

To define the V gene family repertoire of human IgG anti-Haemophilus influenzae type b polysaccharide antibodies, we purified six IgG1 and nine IgG2 anti-Hib-PS antibodies to monoclonality from immune serum of six individuals and performed N-terminal amino acid sequence analysis. Of the 15 clonal antibodies we examined, all H chain V regions were of the VHIII family. In contrast, the L chains of these antibodies were clearly from at least four different VL families; VKI, VKII, VKIII, and V lambda. Interestingly. VL family expression correlated with the cross-reactivity of these antibodies to the capsular carbohydrate of Escherichia coli K100. VKII antibodies did not cross-react, whereas antibodies expressing V lambda, VKI, or VKIII generally cross-reacted. We conclude that L chain V regions are very important contributors to the limited heterogeneity in this antibody repertoire.

Subpopulations of B lymphocytes in germinal centers, II. A germinal center B cell subpopulation expresses sIgD and CD23

To understand B cell development in germinal centers, it is important to delineate the expression of surface antigens among germinal center cells. Because it is unclear whether germinal center cells express common antigens such as sIgD and CD23, we studied their expression among tonsillar lymphocytes with flow cytometry, immunohistochemistry, and in vitro stimulation. Upon studying a large number of tonsils with flow cytometry, we found that occasional tonsils have a very large number of sIgD+ cells among their PNA+ cells. Furthermore, the occasional tonsils with a large number of sIgD+ and PNA+ cells also have many CD23+ cells among their PNA+ cells. Tonsil sections stained immunohistochemically revealed germinal centers containing sIgD+ cells. In addition, PNA- and sIgD+ cells can be induced to express PNA binding sites in vitro without losing the expression of sIgD. Taking these findings together, we conclude that a subpopulation of germinal center B cells coexpresses sIgD and CD23.

Host and bacterial factors associated with Haemophilus influenzae type b disease in Minnesota children vaccinated with type b polysaccharide vaccine

Host and bacterial factors were evaluated among 86 Minnesota children with Haemophilus influenzae type b disease detected by active surveillance after introduction of type b polysaccharide vaccine in the state. Children were 2-6 y of age. Thirty-three (38%) had been vaccinated. There was no significant difference between the frequency of low serum concentrations of IgM, IgA, IgG, or IgG2 in the vaccinated and nonvaccinated subjects (13% vs. 8%, P = .5). The presence of the Gm immunoglobulin allotype phenotype (1,3,17;23;5,13,21), previously associated with a lower relative risk of vaccine failure in children from other states, was associated with a fourfold decrease in the relative risk of vaccine failure in Minnesota (P less than .07). Haemophilus isolates from 58 of the children were available for clonal characterization by multilocus electrophoresis and outer membrane protein subtyping. There were no significant differences between the clone distribution of the strains causing disease in vaccinated and nonvaccinated patients, and nearly all disease-producing clones in Minnesota also are known to cause disease in other areas of the country. Thus, vaccine failure in Minnesota is infrequently associated with hypogammaglobulinemia or with infection by unusual clones of a H. influenzae type b. Also, the Gm phenotype associated with protection against vaccine failure in other areas of the USA appears to be protective in Minnesota.

Clonal characterization of the human IgG antibody repertoire to Haemophilus influenzae type B polysaccharide. Demonstration of three types of V regions and their association with H and L chain isotypes

The antibody response to Haemophilus influenzae type b polysaccharide (Hib-PS) is pauciclonal but can vary between different individuals. To estimate the size of this antibody repertoire we examined the constant and V regions of human IgG anti-Hib antibodies from 14 individuals at the clonal level using various serologic and IEF methods. Examination of H chains showed that 11 of 14 individuals produced both IgG1 and IgG2 antibodies, two individuals produced only IgG2 and one individual produced only IgG1 antibody. All 14 individuals produced kappa-containing antibody clones and three persons also produced significant lambda-containing antibody clones. V region heterogeneity was examined by comparing cross-reactivity of anti-Hib-PS antibodies to the capsular polysaccharide of Escherichia coli K100 carbohydrate (K100 CHO). These studies showed that clones of IgG anti-Hib-PS antibodies cross-reactive with K100 CHO were present in 5 of 14 (36%) individuals and also revealed at least three types of V regions among these antibodies. The first type has no cross-reaction with K100 CHO and was found in 13 of the 14 individuals. The second type, found in three of 14 individuals, cross-reacts with K100 CHO and uses a lambda L chain V region. The third type, found in 2 of 14 individuals, cross-reacts with K100 CHO and uses a kappa L chain V region. Although the lambda type V region was found only in association with IgG2, the other two V region types associate with both IgG1 and IgG2. Thus, five IgG antibody clones are serologically discernable. An individual generally responds to Hib-PS by expressing several clones selected from these discernable antibody clones. Indeed, we can observe six individual response patterns among these 14 individuals and conclude that considerable variability in individual responses to Hib-PS can be achieved with very few V regions.

Clonal characterization of the human IgG antibody repertoire to Haemophilus influenzae type B polysaccharide. Demonstration of three types of V regions and their association with H and L chain isotypes

The antibody response to Haemophilus influenzae type b polysaccharide (Hib-PS) is pauciclonal but can vary between different individuals. To estimate the size of this antibody repertoire we examined the constant and V regions of human IgG anti-Hib antibodies from 14 individuals at the clonal level using various serologic and IEF methods. Examination of H chains showed that 11 of 14 individuals produced both IgG1 and IgG2 antibodies, two individuals produced only IgG2 and one individual produced only IgG1 antibody. All 14 individuals produced kappa-containing antibody clones and three persons also produced significant lambda-containing antibody clones. V region heterogeneity was examined by comparing cross-reactivity of anti-Hib-PS antibodies to the capsular polysaccharide of Escherichia coli K100 carbohydrate (K100 CHO). These studies showed that clones of IgG anti-Hib-PS antibodies cross-reactive with K100 CHO were present in 5 of 14 (36%) individuals and also revealed at least three types of V regions among these antibodies. The first type has no cross-reaction with K100 CHO and was found in 13 of the 14 individuals. The second type, found in three of 14 individuals, cross-reacts with K100 CHO and uses a lambda L chain V region. The third type, found in 2 of 14 individuals, cross-reacts with K100 CHO and uses a kappa L chain V region. Although the lambda type V region was found only in association with IgG2, the other two V region types associate with both IgG1 and IgG2. Thus, five IgG antibody clones are serologically discernable. An individual generally responds to Hib-PS by expressing several clones selected from these discernable antibody clones. Indeed, we can observe six individual response patterns among these 14 individuals and conclude that considerable variability in individual responses to Hib-PS can be achieved with very few V regions.

Alterations in serum immunoglobulin G subclasses in patients with ulcerative colitis and Crohn's disease

We have examined the concentration of immunoglobulin G (IgG) subclass antibodies in the sera of 27 patients with ulcerative colitis and 21 patients with Crohn's disease as well as in 11 normal controls and 11 patients with systemic lupus erythematosus. In comparison with a control mean serum IgG1 concentration of 5173 micrograms/ml, patients with ulcerative colitis exhibited a significantly increased mean serum concentration of 7924 micrograms/ml (p less than 0.05), whereas patients with Crohn's disease had a near normal mean serum IgG1 level of 5898 micrograms/ml. In contrast, control sera had a mean IgG2 level of 2477 micrograms/ml and ulcerative colitis sera had a similar IgG2 level of 2269 micrograms/ml, whereas Crohn's disease sera had a significantly increased mean IgG2 level of 5111 micrograms/ml (p less than 0.05). Patients with systemic lupus erythematosus, like those with ulcerative colitis, had a markedly elevated serum IgG1 level of 15,594 micrograms/ml (p less than 0.001) without a significantly increased IgG2 serum level (3271 micrograms/ml). Neither ulcerative colitis nor Crohn's disease sera exhibited altered levels of IgG3 or IgG4. These data show that alterations in IgG subclass concentrations occur in the sera of patients with active, untreated inflammatory bowel disease, similar to the previously noted changes in the IgG subclasses secreted by lymphocytes from involved inflammatory bowel disease intestinal specimens.

Mitogen-induced human IgG subclass expression. II. IgG1 and IgG3 subclasses are preferentially stimulated by a combination of Staphylococcus aureus Cowan I and pokeweed mitogen

Mitogens generally stimulate human IgG subclass production in amounts proportional to their abundance in serum (IgG1 greater than IgG2 greater than IgG3 greater than IgG4). We report here that a combination of Staphylococcus aureus Cowan strain I and pokeweed mitogen consistently stimulates human peripheral blood lymphocytes in vitro to preferentially produce more IgG1 and IgG3 than IgG2. This preferential stimulation can be measured by increases in the number of immunoblasts (cells with detectable cytoplasmic immunoglobulin) as well as in secreted immunoglobulin. The preferential stimulation pattern is established by the fourth day of culture and is maintained at least until the tenth day. Removal of T cells and subsequent stimulation of B cells with S. aureus Cowan I and interleukin 1 (IL-1) interleukin 2 (IL-2), interleukin 4 (IL-4), or interferon-gamma (IFN-gamma) failed to enhance any IgG subclass production, indicating the requirement for multiple lymphokines in IgG subclass production. The significance of these findings is discussed with respect to B-cell regulatory molecules and the coordinate expression of IgG subclasses.

Antibody secretion by human intestinal mononuclear cells from normal controls and inflammatory bowel disease patients

Inflammatory bowel disease (IBD) intestinal mononuclear cells (MNC) exhibit decreased spontaneous IgA secretion with an increased percentage of monomeric IgA and IgA subclass 1 in both ulcerative colitis and Crohn's disease patients. When compared with control intestinal MNC, a marked increase in spontaneous secretion of IgG is observed from IBD MNC. The greatest increase in spontaneous IgG secretion is seen with ulcerative colitis intestinal MNC, due to the secretion of large amounts of IgG subclass 1. Crohn's disease intestinal MNC have increased IgG subclass 2 secretion. Similar differences in IgG subclass concentrations also occur in the sera of active, untreated, IBD patients. Therefore, major alterations occur with regard to spontaneous antibody secretion of IgA and IgG subclasses in IBD. Because intestinal MNC comprise a unique immunologic compartment, it will be important to better understand the regulatory mechanisms, effector capabilities, and inducing antigens involved in intestinal IgA and IgG subclass secretion in IBD.

Extremely high values of prostate-specific antigen in patients with adenocarcinoma of the prostate; demonstration of the "hook effect"

We reviewed 721 consecutive samples submitted for measurement of prostate-specific antigen (PSA) over five months. We identified three patients with extremely high PSA concentrations: 650, 1840, and 3280 micrograms/L (their acid phosphatase activities were 3.2, 1337, and 2.8 U/L, respectively), and present case reports for the latter two. Serial dilutions of samples obtained from the patient with the highest PSA concentration indicated that the one-step Tandem-PSA assay gave falsely low values for high concentrations of PSA, an observation consistent with the phenomenon of the "hook effect." This effect was not observed when the sample was reanalyzed for PSA by a two-step procedure.