Stress, cortisol, and B lymphocytes: a novel approach to understanding academic stress and immune function

Figures & data

Figure 1. A representative image of the gating procedure. We first used a forward (FSC-H) and side scatter (SSC-A) histogram (a) to gate on the lymphocyte population. Then we used IgG1 FITC-A by IgG1 PE histogram (b) as the negative control. Histogram (c) shows the percentage of CD19 + and CD3 + cells in the lymphocyte gate. The CD19 + subset is shown in histograms (d) and (e).

Table 1. Demographic characteristics of sample.

	Student	Comparison	Statistic	p
N	24	34
Age	27.8 (4.6)	31.8 (9.4)	F(1,56) = 3.78	0.057
Education	17.1 (1.4)	16.8 (1.6)	F(1,56) = 0.44	0.508
Gender			X^2 = 5.50	0.019*
Male	8 (33.3%)	3 (8.8%)
Female	16 (66.7%)	31 (91.2%)
Race/ethnicity			X^2 = 2.35	0.502
White	16 (66.7%)	24 (70.6%)
Hispanic	2 (8.3%)	4 (11.8%)
Asian	5 (20.8%)	3 (8.8%)
Native American	0 (0.0%)	1 (2.9%)
Other	1 (4.2%)	2 (5.9%)
Marital status			X^2 = 4.90	0.086
Single	19 (79.2%)	18 (52.9%)
Partnered	5 (20.8%)	16 (47.1%)

*p < 0.05.

Table 2. Descriptive statistics for all measures among students and community controls at each time point.

	Student		Comparison
	M	SD	M	SD	Statistic	p
T1
Perceived stress	15.83	(7.91)	12.84	(5.58)	F(1,54) = 2.69	0.107
Depressive symptoms	14.87	(10.43)	8.85	(6.81)	F(1,56) = 6.97	0.011*
Negative affect	1.15	(0.82)	0.76	(0.49)	F(1,56) = 5.02	0.029*
% CD19+ lymphocytes	11.75	(3.50)	10.18	(4.57)	F(1,52) = 1.78	0.188
% CD19+ CD10+ lymphocytes	14.89	(5.15)	15.51	(6.43)	F(1,50) = 0.13	0.719
% CD19+ DR + lymphocytes	99.51	(0.64)	99.25	(0.74)	F(1,50) = 1.63	0.207
% CD3+ lymphocytes	74.30	(5.36)	72.01	(6.17)	F(1,52) = 1.92	0.172
PBMC
AUC^a	89.46	(4.82)	95.08	(35.71)	F(1,53) = 0.30	0.584
CAR^a	3.23	(4.82)	5.08	(4.85)	F(1,53) = 1.92	0.172
T2
Perceived stress	16.09	(6.34)	11.23	(6.02)	F(1,51) = 7.91	0.007*
Depressive symptoms	14.09	(10.03)	8.30	(7.90)	F(1,51) = 5.43	0.024*
Negative affect	1.19	(0.69)	0.73	(0.57)	F(1,51) = 6.81	0.012*
% CD19+ lymphocytes	10.21	(2.67)	11.79	(4.72)	F(1,51) = 1.92	0.172
% CD19+ CD10+ lymphocytes	17.23	(7.86)	19.39	(8.47)	F(1,51) = 0.86	0.358
% CD19+ DR + lymphocytes	99.16	(0.67)	99.30	(0.86)	F(1,51) = 0.40	0.528
% CD3+ lymphocytes PBMC	69.82	(6.97)	72.20	(9.61)	F(1,51) = 0.95	0.334
AUC^a	87.41	(37.11)	98.03	(36.40)	F(1,51) = 1.06	0.308
CAR^a	0.33	(4.35)	3.66	(5.43)	F(1,51) = 5.62	0.022*

^a One participant was excluded from these analyses as the individual’s T1 cortisol levels were deemed an outlier during normality analyses. T2 cortisol levels were not collected for this participant.

*p < 0.05.

Figure 2. Change in CD19 + B Lymphocytes over time among students and community comparison participants. Student status predicted a significant decrease in CD19 + lymphocyte percentage when controlling for T1 CD19 + percentage and T2 PBMC (β = 0.275, *R² = 0.061, p = 0.025). *p < 0.05.

Figure 3. Flattening of CAR from T1 to T2 among students compared to community comparison group (mean of T1 and T2). Note: *indicates that Student T2 salivary cortisol is significantly lower than student salivary cortisol levels at T1 or the community mean.

Table 3. Summary of hierarchical linear regression analyses.

T2 outcome variable^a	R^2	β	ΔR^2	F of ΔR^2	p
Perceived stress	0.475	−0.332	0.085	7.096	0.011*
Depressive symptoms	0.342	−0.145	0.015	1.017	0.319
Negative affect	0.314	−0.241	0.041	2.782	0.102
CD19+ lymphocytes^b	0.487	0.275	0.061	5.427	0.025*
CD19+ CD10+ lymphocytes^b	0.253	0.157	0.020	1.048	0.312
CD19+ DR + lymphocytes^b	0.167	0.205	0.032	1.508	0.227
CD3+ lymphocytes^b	0.518	0.214	0.032	2.740	0.105
PBMC	0.036	0.072	0.004	0.179	0.674
Cortisol AUC	0.402	0.205	0.034	2.683	0.108
CAR	0.125	0.313	0.076	4.085	0.049*
CD19+ lymphocytes^c	0.588	−0.240	0.056	5.474	0.024*

^a All regression equations controlled for T1 of the outcome variable of interest in the first block of the equation and age and gender in block two. Group (student or community comparison) was in the third block of the model.

^b Regression equations for lymphocytes also controlled for T2 PBMC in the second block of the equation.

^c Change in CAR was included as a predictor in the fourth block of the model.

*p < 0.05.