Risk of classical Kaposi sarcoma by plasma levels of Epstein-Barr virus antibodies, sCD26, sCD23 and sCD30

Kaposi sarcoma (KS) develops in develops in a minority of people who have been infected with Kaposi sarcoma-associated herpesvirus (KSHV). KS is the predominant malignancy occurring in people with the acquired immunodeficiency syndrome (AIDS), illustrating that cell-mediated immunity modifies the risk KS. However, the abnormalities with AIDS are so varied in type and severity that dissecting those specifically associated with KS is challenging. Studies of people who do not have overt immunologic abnormalities may be more informative, although consistent, unambiguous perturbations have yet to be reported in non-AIDS KS [1‐4].

KSHV reactivation with viremia is predictive for KS [5], but study of the underlying immunologic mechanisms is technically difficult and unsettled [6‐8]. In lieu of a KSHV-specific approach, generic measures of immunity may be helpful. Loss of immunologic control of the related gammaherpesvirus, Epstein-Barr virus (EBV), results in viral reactivation and is marked by higher antibodies against viral capsid antigen (anti-VCA) and lower antibodies against nuclear antigen-1 (anti-EBNA-1). This EBV serology pattern, as well as altered levels of soluble cluster of differentiation (sCD) markers (sCD26, sCD23 and sCD30), have been associated with immune-mediated clinical conditions [9‐14]. The Th1/Th2 cellular immunity paradigm has been the rationale [9‐14]. We examined whether these markers were associated with classical KS (cKS) in a population-based study in Sicily.

We included 119 cKS cases, 105 KSHV seropositive controls, and 155 KSHV seronegative controls (Table 1). Anti-EBNA-1 levels ranged from 0.59 - 9.59, and anti-VCA from 0.87 - 9.47. High-tertile anti-VCA was associated with KSHV seropositivity among controls (Table 2, lower panel), but overall anti-EBV levels were not correlated with anti-KSHV levels (Pearson R ≤ 0.07, P≥0.29). Radiation and chemotherapy history in cases was infrequent and unrelated to anti-EBV and sCD levels. Excluding such cases did not substantially alter the results (data not shown).

Mean [standard deviation (SD)] anti-EBNA-1 levels were 5.39 (SD 1.93) in cases, 5.56 (SD 1.72) in seropositive controls, and 5.25 (SD 1.78) in seronegative controls. Mean anti-VCA levels were 5.53 (SD 1.68) in cases, 5.71 (SD 1.82) in seropositive controls, and 5.40 (SD 1.69) in seronegative controls. Adjusted for age and sex, mean differences between cases and seropositive controls were -0.23 [95% confidence interval (CI): -0.70, 0.24] for anti-EBNA-1 and -0.25 (95% CI: -0.72, 0.22) for anti-VCA. With further adjustment for cKS cofactors, anti-EBV levels were virtually identical (mean difference 0.02 for anti-EBNA-1, 0.03 for anti-VCA). Anti-EBV levels did not confound or modify the associations of the cofactors with cKS (data not presented) [15]. Only 5 cases and 6 seropositive controls had low-EBNA-1/high-VCA, which was associated with a non-significantly lower risk of cKS (Table 2, upper panel).

Comparing KSHV-seropositive versus -seronegative controls, adjusted for age and sex, mean differences were 0.34 (95% CI: -0.11, 0.80) for both anti-EBNA-1 and anti-VCA. With further adjustment for cKS cofactors, mean differences were 0.21 (95% CI: -0.24, 0.66) and 0.18 (95% CI: -0.26, 0.62) for anti-EBNA-1 and anti-VCA, respectively.

In the combined group of controls, levels of anti-EBNA-1 and especially anti-VCA were substantially and significantly lower with three cKS cofactors: male sex, nonsmoking, and diabetes (Table 3). The anti-EBNA-1 and anti-VCA levels also were marginally lower with the fourth cKS cofactor, cortisone use (Table 3).

Considering cKS cofactors in the control subjects, sCD26 levels were higher in females (median 459 ng/mL vs 416 ng/mL, P_adj = 0.006) and current smokers versus never smokers (median 508 ng/mL vs 425 ng/mL, P_adj = 0.03); and sCD26 levels tended to be lower in cortisone users (median 422 ng/mL vs 446 ng/mL, P_adj = 0.09). Older controls tended to have lower sCD26 (P_adj = 0.06) and higher sCD30 (P_adj = 0.08) levels. Otherwise, cKS cofactors were not associated with sCD levels (P_adj > 0.09, data not presented).

Our assays have been used as measures of immunity for epidemiologic research, specifically invoking the Th1/Th2 cellular immunity paradigm [9, 10, 16]. However, in vitro data to support their use are sparse. Especially with a single plasma sample, these assays may be too crude to distinguish a chronic condition, such as cKS, with the limited statistical power that we had herein.

Although cases did not differ from controls, our findings on cKS cofactors among controls should be noted, particularly because these cofactors are also associated with Th1/Th2 alteration. Th1 responses are generally lower and Th2 responses generally higher in women, smokers, diabetics, and corticosteroid users [17‐22]. Classical KS risk is increased for corticosteroid users and perhaps diabetics, but cKS risk is reduced for women and smokers [15, 23]. The effect of smoking on Th1/Th2 cytokine levels may also differ by sex [24]. These complex and even inverse relationships suggest that differences in cKS risk may reflect differences in immunity or inflammation that are captured, but only weakly, by anti-EBV and sCD26 levels.

The parent case-control study, including KSHV serostatus definition, has been reported [15]. The current study included all cKS cases, all KSHV-seropositive controls, and a sample of KSHV-seronegative controls with ≥0.5 mL previously unthawed plasma for the assays. Seronegatives were matched to seropositive controls and cases on cKS cofactors (sex, age group, cigarette smoking and diabetes).

EBV enzyme immunoassays were performed as described [25]. Antibody levels were the ratio of each specimen's average optical density (OD₄₅₀) divided by the average OD₄₅₀, plus 2 standard deviations, of four negative controls on each plate. Ratio value is highly correlated with anti-EBV immunofluorescence end-point titer [25]. Commercial kits were used to quantify sCD26, sCD23 and sCD30 [Bender MedSystems GmbH (Vienna, Austria)].

Three sets of comparisons were made: cKS cases versus KSHV-seropositive controls; KSHV-seropositive versus-seronegative controls; and all controls by cKS-related cofactors (including KSHV serostatus). We used linear regression (for anti-EBV levels) or Mann-Whitney-Wilcoxon (for sCD levels) methods. As done previously [8, 9], cKS risk was postulated to be highest with low-EBNA-1/high-VCA, defined using tertiles among controls. Odds of cKS was estimated with unconditional logistic regression and with conditional logistic regression, conditioning on assay batch.