High-level ability of secretory IgA to block HIV type 1 transcytosis: contrasting secretory IgA and IgG responses to glycoprotein 160.

The IgG and secretory IgA (S-IgA) responses to the HIV-1 envelope (gp160 antigen) were analyzed in the colostrum (Col) and in the cervicovaginal fluid (CVF) of HIV-l-infected women. We show IgG antibodies (Abs) to the recombinant gp160 to be predominant as compared with the corresponding S-IgA isotype. The low level of the S-IgA response cannot be related to a general disturbance of the mucosal-associated Iymphoid tissue (MALT) because the level of a current Ab to a caries-associated antigen from Streptococcus sobrinus was in the normal range in these secretions. The major subclass of IgA to gp160 was of the alpha1 isotype both in Col and in CVF. However, the specific activities of S-IgA1 and S-IgA2 were different when expressed as the ratio of the anti-gp160 related to total Ig of each subclass. Indeed, the specific activity of the S-IgA2 was predominant over S-IgA1 in the Col, whereas the reciprocal results were found in CVF, showing a subcompartmentalization of these secretions. The ability of S-IgA and IgG to block one of the pathways involved in the HIV-1 penetration across mucosa, i.e., transcytosis through epithelial cells, was evaluated using a functional in vitro assay. Both S-IgA and IgG Abs impaired virus transcytosis, irrespective of the level of antigp160 specific activities. However, specific S-IgA was more efficient than IgG. These features suggest that mucosal specific S-IgA to HIV-1 could be relevant in decreasing infectivity of HIV-1 in corporal fluids.

A simple procedure for the isolation of human secretory IgA of IgA1 and IgA2 subclass by a jackfruit lectin, jacalin, affinity chromatography.

Jackfruit lectin, jacalin, prepared from two batches of jackfruit seeds showed a different specificity in precipitating reaction in Agarose gel with various purified immunoglobulins and secretory components. Jacalin-P, extracted from jackfruit seeds from the Philippines, reacts only with serum IgA and secretory IgA of IgA1 subclass. Jacalin-O, extracted from jackfruit seeds from Okinawa prefecture in Japan, makes a strong precipitin are with IgA1 subclass and a weak precipitin arc with IgA2 subclass of IgA2m(2) allotype, IgM, IgD and IgE. Human secretory IgA of IgA1 subclass was isolated from human milk by a single jacalin-P affinity chromatography using D-galactose as a dissociating agent. From conventionally purified human secretory IgA preparation, secretory IgA of IgA1 subclass and of IgA2 subclass were separated from each other. The former was separated as jacalin-P adsorbed fraction and the latter as jacalin-P non-adsorbed fraction by the affinity chromatography. Subclass composition of secretory IgA in human milk was determined by the affinity column and was calculated to be 70% for IgA1 and 30% for IgA2 subclass. Jacalin affinity chromatography has several advantages compared with antibody coupled affinity chromatography, notably, high capacity, inexpensiveness, and very mild extraction of IgA1 subclass.

Separation of human IgA1 and IgA2 using jacalin-agarose chromatography.

A lectin isolated from the tropical jackfruit, jacalin, previously reported to precipitate human immunoglobulin A (IgA), and conjugated to agarose was used to separate the two subclasses of IgA from secretions. Jacalin-agarose binds specifically to the D-galactose moiety of IgA1 but not to IgA2 which has a different carbohydrate content and structure. IgA2 passed through the jacalin-agarose column and was collected in the void volume. IgA1 was eluted from the lectin by 0.8 M galactose. Of a representative diluted anti-alpha chain-purified colostral IgA preparation containing 50.2 micrograms IgA1 and 55.8 micrograms IgA2, 40.3 micrograms IgA1 (80.3% of the original) and 49.6 micrograms IgA2 (88.9%) was collected following jacalin-agarose chromatography. The jacalin-purified IgA1 fraction contained 8.0% IgA2 and the IgA2 fraction contained no IgA1. In addition, the IgA1 and IgA2 fractions had naturally occurring antibody activity to a normal oral bacterium. The method is easy, reproducible and specific and has many applications to mucosal immunological investigations.