The Early Humoral Response in Human Granulocytic Ehrlichiosis

Abstract

The early antibody response in patients with human granulocytic ehrlichiosis (HGE) and in mice infected with the HGE agent was characterized by using sera to probe lysates of HL-60 cells infected with HGE organisms. Sera were obtained from 18 patients with HGE, mostly within the first 6 weeks of clinical infection, and from mice infected with the HGE agent for up to 3 weeks. A 44-kDa antigen was reactive with IgG in all 18 patients, and IgG to 40-, 65-, and 80-kDa antigens was present in 6, 8, and 7 patients, respectively. In addition, IgM to 40-, 44-, 65-, and 80-kDa antigens was found in 9, 5, 4, and 4 subjects. Immunoglobulins to antigens ranging between 95 and 125 kDa were detected less frequently. HGE agent-infected C3H/HeJ mice had an antibody response similar to that in humans. Thus, the 40- and 44-kDa proteins of the HGE agent elicit early strong antibody responses during infection. Characterization of the antigens recognized by antibodies during HGE should aid in diagnosis and understanding of the disease.

Antibodies to granulocytic ehrlichiae in cattle from Connecticut

“…This strain, originally isolated from a human patient in Nantucket, MA, USA, and grown in human promyelocytic leukaemia cell (HL-60, American Type Culture Collection CCL-240) cultures, has been used extensively in serological testing [11,19,21,22]. Serum samples were diluted to 1 in 80 in phosphatebuffered saline (PBS; pH 7.2) and placed in 12-ìl volumes over each antigen preparation on glass microscope slides.…”

“…After incubation and washing, slides were examined by fluorescence microscopy. Positive horse, deer (cervid) and human serum samples, obtained from subjects naturally exposed to the HGE agent or E. equi and who had the DNA of the HGE agent in blood samples [11][12][13]19], were used to verify antigen reactivity. The antibody-positive deer serum sample was also used to check reactivity of the conjugated anti-bovine antibodies; deer are closely related to bovids.…”

“…It was particularly important to confirm serological reactivity of positive sera to the p44 antigen of the HGE agent, a specific marker for HGE and EGE infections. Generally, immunoblotting procedures used before [19,21] were employed in analyses of serum samples from cattle. Lysates of HL-60 cells infected with the NCH-1 strain of the HGE agent were included as antigen.…”

“…Materials and methods used to detect the DNA of the HGE agent in whole blood samples from human patients [19], white-tailed deer [11] and horses [12,13] were applied in analysis of nine EDTA-treated whole blood samples from nine cattle. Blood samples were collected from these animals in tick-infested areas of five towns during December 1999 and February 2000.…”

“…In European studies of infected cows, decreased milk production was noted [17]; E. phagocytophila was detected in leucocytes from milk samples obtained during the acute phase of disease [18]. Although there are numerous reports on HGE in the USA [6,7,[14][15][16]19], little is known about patterns of immune responses, antibody production and seroprevalence of granulocytic ehrlichial infections in cattle. Preliminary studies revealed that cattle living in tick-infested areas of Connecticut, USA, had antibodies to the HGE agent.…”