GC Reaction Research Articles

Role of complement receptors CD21/CD35 in B lymphocyte activation and survival.

In summary, the complement system has evolved an important function in regulation of humoral immunity to T-dependent antigens. Covalent attachment of activated C3 to antigen alters its fate by enhancing uptake on the surface of FDC via CD21/CD35; and by enhancing signal transduction via the B cell coreceptor CD21/CD19/Tapa-1. In the absence of complement receptors CD21/CD35 or C3 ligand, naive B cells bearing low affinity BCR fail to effectively survive within the lymphoid follicle following contact with antigen and death is mediated by a Fas-dependent mechanism. Alternatively, B cells sufficiently activated to initiate a GC reaction fail to survive in the absence of CD21-CD21L interaction.

Screening for gonorrhea and chlamydia by DNA amplification in adolescents attending middle school health centers. Opportunity for early intervention.

To determine prevalence and incidence of Neisseria gonorrhoeae (GC) and Chlamydia trachomatis (CT) infection and assess risk factors predictive for such infections in a middle school-based clinic sample. 170 female students and 43 male students making 256 and 47 visits, respectively, > or = 30 days apart, in urban middle school clinics for primary care screening, reproductive health, or illness/injury were routinely asked to provide urine specimens for GC and CT ligase chain reaction testing if sexually active in the preceding 3-month period. Information regarding prior sexually transmitted diseases, reason for visit, and sexual risk behaviors was obtained. GC: 11.4% of female student and 2.1% of male student tests were positive. Incidence was 34.0 cases/1,000 person months (95% Confidence interval [CI]: 19.5-67.5). Median time to first positive and repeat positive test was 4.6 and 2.6 months, respectively. For CT: 16.4% of female student and 2.1% of male student tests were positive. Incidence was 57.5 cases/1,000 person months (95% CI: 35.2-93.8). Median time to first positive and repeat positive CT test was 6.0 and 4.8 months, respectively. Assessed risk factors failed to specify a candidate screening population. These data suggest that all sexually active adolescent girls in this high risk setting should be offered testing for GC and CT at least twice per year, regardless of age or other sexual risk behaviors and that STD control efforts in high risk middle schools should be encouraged.

Somatic hypermutation in normal and transformed human B cells.

In the human, most IgM+IgD+ as well as CD5+ peripheral blood B cells express unmutated V genes and thus can be assigned to a pre-germinal centre (GC) stage of development. The memory B-cell compartment generated in the GC reaction and characterized by cells bearing somatically mutated V-region genes consists not only of class-switched cells, but also of IgM-only B cells and perhaps a subset of IgM+IgD+B cells expressing the CD27 antigen. Comparison of the rearranged V-region genes of human B-cell lymphomas with those of the normal B-cell subsets allows the identification of the progenitor cells of these tumours in terms of their stage of maturation. On this basis, most B-cell non-Hodgkin lymphomas, and in addition Hodgkin and Reed-Sternberg (HRS) cells in Hodgkin's disease (HD), are derived from B cells at a GC or post-GC stage of development. The mutation pattern indicates that the precursors of the tumour clones have been stringently selected for expression of a functional antigen receptor with one notable exception: HRS cells in classical (but not lymphocyte-predominant) HD appear to be derived from "crippled" GC B cells. Sequence analysis of rearranged V genes amplified from single tonsillar GC B cells revealed that the somatic hypermutation process introduces deletions and/or insertions into V-region genes more frequently than indicated by previous investigations. Presumably, this feature of the hypermutation mechanism is often responsible for the generation of heavy chain disease, and also several types of chromosomal translocations of oncogenes into immunoglobulin loci in human B-cell lymphomas.

A Periarteriolar Lymphoid Sheath-Associated B Cell Focus Response Is Not Observed During the Development of the Anti-Arsonate Germinal Center Reaction

The behavior of p-azophenylarsonate (Ars)-specific B cell clones during the primary T cell-dependent splenic response of A/J mice was investigated using an immunohistochemical approach. The earliest Ars-specific B cells were observed as isolated cells in the red pulp by day 3 after immunization with Ars-keyhole limpet hemocyanin, (KLH) and at day 6, large clusters of Ars-specific B cells were first detected in germinal centers, which continued to be observed for an additional 8 to 15 days. Surprisingly, no Ars-specific B cell foci were observed in or near the CD4 T cell-rich periarteriolar lymphoid sheath (PALS) during the entire primary response. Nevertheless, A/J mice immunized with (4-hydroxy-3-nitrophenyl)acetyl-chicken gamma globulin (NP-CGG) or Ars-CGG mounted robust splenic (4-hydroxy-3-nitrophenyl)acetyl or CGG-specific PALS-associated focus reactions, respectively. In contrast, no Ars-specific PALS B cell foci were detected in A/J mice immunized with Ars-CGG. These data add to a growing body of evidence indicating that B cell proliferation and differentiation in CD4 T cell-rich microenvironments are not prerequisites for the GC reaction. Taken together with previous results obtained using other model Ags, the data suggest that the specificity of the B cell Ag receptor may strongly influence the lymphoid microenvironment in which a B cell clone first undergoes Ag-driven clonal expansion and differentiation.

The preference for switching to expression of the IgA isotype of antibody exhibited by B lymphocytes in Peyer's patches is likely due to intrinsic properties of their microenvironment

The prompt switching to the expression of different non-IgM/IgD isotypes in PP and LN during acute, de novo GC reactions at the two types of sites suggests intrinsic differences in their microenvironments as the basis for isotype preference.

Endogenous gibberellins and inhibitors in the Douglas-fir

In young needles of the Douglas-fir (Pseudotsuga menziesii) GA9 has been shown by GC and HPLC to be the main gibberellin. As minor compounds GA7, GA3 and GA8 have been tentatively identified by HPLC. In addition to the free gibberellins small amounts of GA9 glucosyl ester and a not yet identified ester of GA20 have been isolated. From the group of endogenous inhibitors ABA has been identified by GC-MS and ABA glucosyl ester by HPLC. After enzymatic hydrolysis of the ester, ABA and glucose have been quantified by GC and GOD-POD reaction giving the ratio 1:1. Another plant growth inhibitor has been identified as the methyl ester of jasmonic acid.