No abstract

Although the switch process is frequently associated with affinity maturation, the constant region is not assumed to play a role in Ag-Ab binding. In the present work, we demonstrate that two clonally related human monoclonal Igs sharing identical V H and V L sequences, but expressing different isotypes (IgA1 PER and IgG1 PER ), bind tubulin with significantly different affinities. This difference was mainly accounted for by a disparity in the association rate constants. These results suggest that affinity maturation of this clone could be achieved through class switching in the absence of further somatic mutations. Since the differences observed were found at the Fab level, they also suggest a role for the C H 1 domain in structuring the Ag-binding site into a more kinetically competent form. ( J. Clin. Invest. 1996. 98:2235-2243.)

No abstract

Secretory immunoglobulin A (S-IgA) was investigated in human secretions for the presence of natural antibodies (Abs) acting as the first "immune barrier" to infection before induction or boosting of specific responses. These molecules could be the secretory counterpart of the natural Abs in serum that were previously shown by our laboratory to be polyreactive to autoantigens. Significant levels of S-IgA Abs to human actin, myosin, tubulin, and spectrin were detected in 10 saliva and 8 colostrum samples from normal subjects. Computer-assisted analysis of immunoblots of extracts from human muscles showed these Abs to react with a large number of autoantigens. Their polyreactivity was confirmed by cross-inhibition and by immunoblotting studies of affinity-purified natural Abs, assayed against a large variety of surface or secreted antigens from Streptococcus pyogenes. The thiocyanate elution method showed that functional affinities of some natural Abs can be of the same order of magnitude as those of tetanus vaccine antitoxins. Moreover, nonimmune binding of these natural Abs to the gut protein Fv (Fv-fragment binding protein) can enhance their effector functions. This demonstrates that human secretions contain polyreactive auto-Abs which can also react with pathogens. These secretory Abs of "skeleton key" specificities are possibly produced by a primordial B-1-cell-associated immune system and can be involved in a plurispecific mucosal protection against pathogens, irrespective of the conventional immune response.

No abstract

The molecular status of Abs in the vaginal fluid is reconsidered as a basis for immunization strategies for women' vaccination against HIV. Analysis of separated immunoglobulins (Igs) shows a large proportion of uncleaved IgG, whereas the low amount of IgA includes SIgA, monomers and fragments. SIgM is at a very low level, while free SC molecules are abundant. In addition to the already documented local synthesis, vaginal IgG contains serum-derived tetanus antitoxins. The IgG could reach the lumen by diffusion, and/or be transported by an Fc receptor-associated mechanism as suggested by the subclass imbalance in favour of the IgG1 isotype. VAginal SIgA contains very low levels of antibodies o the cell-well carbohydrates from a dental caries-associated streptococcus confirming the participation of the secretory immune system. IN addition, the low percentage of IgA2 suggests tha a proportion of vaginal SIgA can also derive from actively transported serum polymers. In agreement with our previous studies showing induction of vaginal tetanus antitoxins by intramuscular immunization, these results are in favour of classical, parenteral vaccinations to induce protection of the human vagina.

Four different monoclonal Ig (MIg) (IgA1κ, IgG1κ, IgG2κ and IgG4κ) displaying anti‐tubulin activity were detected in the serum from a lymphoma patient. The complete sequence of three of these MIg showed identical VH and VL domains and the presence of mutations compatible with an antigen‐driven process. Surprisingly, despite complete homology in their variable domains, IgA1κ, IgG1κ, or their Fab fragments bound to a common motif recognized in β tubulin, with significant differences in affinity (IgA1κ 1.52×10–8 M, and IgG1κ 2.09×10–7 M). To substantiate these results, the VH and VL domains from IgA1κ were cloned and introduced into expression vectors containing the constant κ exon and either the μ or the γ1 constant exon, and complete recombinant IgMκ and IgG1κ were obtained. Like the IgA1κ, the IgMκ construction bound to the tubulin epitope with consistent affinity (7.7×10–9 M), whereas the IgG1κ construction displayed a significantly lower affinity (3.28×10–7 M). These results provide definitive evidence that isotype can influence binding affinity to antigen and suggest that malignant transformation occurred at the germinal center once the mutational process was achieved and the switch process was still active.

OBJECTIVE: To explain the high frequency of heterosexual transmission of AIDS in subSaharan countries, by investigating post-intercourse semen retention in the vagina for local pH neutralization as a possible interference factor with acidic inactivation of HIV virions. METHODS: Two semen markers, prostate-specific antigen and prostatic acid phosphatase, were measured and compared with the pH values in the vaginal washes of 69 women from the Central African Republic. The capacity of semen to raise the vaginal pH was also investigated in vitro. RESULTS: Of 61 non-menstrual specimens, 74% contained at least one semen marker. The specimens with high levels of markers (group I) displayed an almost neutral pH (median 6.1), at variance with the semen-free group II (median: 3.7, P<0.003), and with group III (median: 4.0) corresponding to low or past semen retention. The in vitro study confirmed the high neutralization capacity of semen. CONCLUSIONS: It is expected that post-intercourse neutralization of pH will both favor male-to-female transmission and prevent the acidity-associated loss of infectivity of the female-derived virions, thus allowing female-to-male transmission during further sexual contact.