Casein-hydrolyzing activity of sIgA antibodies from human milk

Abstract

During pregnancy and immediately after delivery (i.e. at the beginning of lactation), the female organism is frequently characterized by an immune status similar to that of patients with autoimmune diseases. In addition, lactation is associated with an appearance of catalytically active antibodies or abzymes (Abzs) with DNAse, RNase, ATPase, amylolitic, protein kinase and lipid kinase activities in breast milk. However, until now there were no examples of human milk Abzs with a proteolytic activity. We present the first evidence that electrophoretically and immunologically homogeneous human milk sIgAs possess a beta-casein-hydrolyzing activity different from known proteases. Abzs specifically hydrolyze both human and bovine beta-caseins but not many other proteins tested. Using different methods including in situ analysis of proteolytic activity in a gel after SDS-PAGE it was shown that the observed proteolytic activity is an intrinsic property of human milk polyclonal sIgAs. Specific inhibitors of acidic and thiol proteases demonstrated a weak effect on proteolytic activity of Abzs, while a specific inhibitor of serine proteases (AEBSF) significantly inhibited the proteolytic activity of the abzymes. The K(M) value for human casein as a substrate was estimated (7.3 microM). Our findings suggest that the immune system of clinically healthy mothers can generate IgAs with a beta-casein-specific serine protease-like activity.

Anti‐histone H1 IgGs from blood serum of systemic lupus erythematosus patients are capable of hydrolyzing histone H1 and myelin basic protein

“…It was found that both types of protease inhibitors significantly suppressed the hydrolysis of histone H1 (Figure 6, lanes 1 and 2) and bMBP ( Figure 6, lanes 5, 6) in the presence of anti-histone H1 IgGs isolated from blood serum of SLE patients. Thus, similarly to other catalytically active Ab found in human blood serum and milk (Ponomarenko et al, 2002;Odintsova et al, 2005;Kit et al, 2008), IgG-protabzymes isolated from blood serum of SLE patients and capable of hydrolyzing histone H1 and bMBP, belong to serine proteases.…”

Catalytic Antibodies in Norm and Systemic Lupus Erythematosus

“…Protease IgGs from the sera of ~95-100% of patients with different autoimmune pathologies [9,66,116], human milk Abs hydrolyzing casein [96,117], Abs from AIDS patients hydrolyzing HSA, casein, and HIV reverse transcriptase [95] are serine-like proteases, whose activity is strongly decreased after their preincubation with serine protease-specific inhibitors PMSF. In addition, a high metal-dependent MBP-hydrolyzing activity for MS IgGs [86] and caseinhydrolyzing of human milk sIgAs [96] were recently revealed.…”

Natural Catalytic Antibodies in Norm and in HIV-Infected Patients

“…At the same time, the relative rate of -casein hydrolysis was 9-and 550-fold higher than that for HIV RT and HSA, respectively. The K m for casein ((7.3±1.2)×10 -6 M; k cat = 0.75±0.05 min -1 ) estimated in the reaction catalyzed by polyclonal sIgAs from human milk (Odintsova et al, 2005) is comparable with that for IgGs from AIDS patients, while the k cat is ~38-fold higher. This difference is most likely due to a higher content of anticasein proteolytic Abzs in human milk in comparison with blood of AIDS patients.…”

“…Casein hydrolyzing Abzs was found not only in the sera of HIV-infected patients (Odintsova et al, 2006 b ) but also in the milk of lactating women (Odintsova et al, 2005;2011). At the first glance, no obvious immunizing factors could be found in clinically healthy pregnant and lactating women.…”